diff --git a/.tool-versions b/.tool-versions
index d73a169..f4eb891 100644
--- a/.tool-versions
+++ b/.tool-versions
@@ -6,3 +6,4 @@ copilot-cli 1.0.69
 squad-cli 0.10.0
 gh 2.92.0
 delta 0.19.2
+lazygit 0.63.0
diff --git a/scripts/linux/tools/lazygit.sh b/scripts/linux/tools/lazygit.sh
new file mode 100644
index 0000000..d751391
--- /dev/null
+++ b/scripts/linux/tools/lazygit.sh
@@ -0,0 +1,81 @@
+#!/usr/bin/env bash
+# scripts/linux/tools/lazygit.sh -- Install lazygit (terminal UI for git) at pinned version
+#
+# Called by: scripts/linux/setup.sh
+# Idempotent: yes -- version-aware; upgrades if installed version != pinned version.
+# Opt-in: NOT in DEFAULT_TOOLS; only runs when requested via --only=lazygit.
+#
+# macOS: brew install lazygit (warns if brew version differs from pin).
+# Linux: downloads the pinned release tarball from GitHub releases.
+#   Asset naming: lazygit_<version>_linux_x86_64.tar.gz (no leading v; lowercase os/arch).
+#   Binary is at the archive root -- extract and install to ~/.local/bin.
+#   Note: Ubuntu PPA lags significantly; tarball is primary for version accuracy.
+
+# shellcheck disable=SC1091
+. "$(dirname "${BASH_SOURCE[0]}")/../lib/log.sh"
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+LG_VERSION="$(sh "${SCRIPT_DIR}/../../lib/read-tool-version.sh" lazygit)"
+
+if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
+  set -euo pipefail
+
+  # Detect installed version
+  INSTALLED_VERSION=""
+  if command -v lazygit &>/dev/null; then
+    INSTALLED_VERSION="$(lazygit --version 2>&1 | grep -oE '[0-9]+\.[0-9]+\.[0-9]+' | head -1 || true)"
+  fi
+
+  if [ "${INSTALLED_VERSION}" = "${LG_VERSION}" ]; then
+    log_ok "lazygit already at pinned version ${LG_VERSION}"
+    exit 0
+  fi
+
+  if [ -n "${INSTALLED_VERSION}" ]; then
+    log_info "lazygit ${INSTALLED_VERSION} installed; upgrading to pinned ${LG_VERSION}..."
+  else
+    log_info "Installing lazygit ${LG_VERSION}..."
+  fi
+
+  PLATFORM="$(uname -s)"
+  if [[ "$PLATFORM" == "Darwin" ]]; then
+    # Homebrew: versioned formulae for lazygit are not reliably pinnable.
+    if command -v lazygit &>/dev/null; then
+      brew upgrade lazygit || true
+    else
+      brew install lazygit
+    fi
+    ACTUAL_VERSION="$(lazygit --version 2>&1 | grep -oE '[0-9]+\.[0-9]+\.[0-9]+' | head -1 || echo 'unknown')"
+    if [ "${ACTUAL_VERSION}" != "${LG_VERSION}" ]; then
+      log_warn "lazygit ${ACTUAL_VERSION} installed (pinned: ${LG_VERSION}); brew cannot guarantee exact version"
+    else
+      log_ok "lazygit installed at ${LG_VERSION}"
+    fi
+  else
+    # Linux: tarball from GitHub releases (asset names use lowercase os/arch, no leading v).
+    ARCH="$(uname -m)"
+    case "$ARCH" in
+      x86_64)        ARCH_SUFFIX="x86_64" ;;
+      aarch64|arm64) ARCH_SUFFIX="arm64" ;;
+      *)             log_error "Unsupported architecture: ${ARCH}"; exit 1 ;;
+    esac
+
+    TARBALL="lazygit_${LG_VERSION}_linux_${ARCH_SUFFIX}.tar.gz"
+    TARBALL_URL="https://github.com/jesseduffield/lazygit/releases/download/v${LG_VERSION}/${TARBALL}"
+    INSTALL_DIR="${HOME}/.local/bin"
+    WORK_DIR="${HOME}/.local/share/dev-setup-install/lazygit"
+
+    mkdir -p "$INSTALL_DIR"
+    mkdir -p "$WORK_DIR"
+
+    log_info "Downloading ${TARBALL}..."
+    curl -fsSL "$TARBALL_URL" -o "${WORK_DIR}/${TARBALL}"
+    # Binary is at the archive root (no version-named subdirectory).
+    tar -xzf "${WORK_DIR}/${TARBALL}" -C "$WORK_DIR"
+    cp "${WORK_DIR}/lazygit" "${INSTALL_DIR}/lazygit"
+    chmod +x "${INSTALL_DIR}/lazygit"
+    rm -rf "$WORK_DIR"
+
+    log_ok "lazygit ${LG_VERSION} installed to ${INSTALL_DIR}/lazygit"
+  fi
+fi
diff --git a/scripts/windows/setup.ps1 b/scripts/windows/setup.ps1
index c5bac3d..4634ce8 100644
--- a/scripts/windows/setup.ps1
+++ b/scripts/windows/setup.ps1
@@ -47,6 +47,7 @@ $ErrorActionPreference = 'Stop'
 . "$PSScriptRoot\tools\auth.ps1"
 . "$PSScriptRoot\tools\git-hook.ps1"
 . "$PSScriptRoot\tools\delta.ps1"
+. "$PSScriptRoot\tools\lazygit.ps1"
 
 # ---------------------------------------------------------------------------
 # $DefaultTools -- single ordered source of truth for a no-arg default run.
@@ -87,6 +88,7 @@ $ToolRegistry = [ordered]@{
     'profile'      = { Write-PowerShellProfile }
     'git-hook'     = { Install-GitHook }
     'delta'        = { Install-Delta }
+    'lazygit'      = { Install-Lazygit }
 }
 
 # ---------------------------------------------------------------------------
diff --git a/scripts/windows/tools/lazygit.ps1 b/scripts/windows/tools/lazygit.ps1
new file mode 100644
index 0000000..80ccfe1
--- /dev/null
+++ b/scripts/windows/tools/lazygit.ps1
@@ -0,0 +1,53 @@
+# scripts/windows/tools/lazygit.ps1 - lazygit installer
+#
+# Installs lazygit at pinned version from .tool-versions.
+# Opt-in: NOT in $DefaultTools; only runs when requested via -Only 'lazygit'.
+# winget preferred (id JesseDuffield.lazygit); scoop fallback when winget unavailable.
+# PS 5.1 ASCII-only: no smart quotes, em-dashes, or non-ASCII characters.
+
+Set-StrictMode -Version Latest
+$ErrorActionPreference = 'Stop'
+
+. "$PSScriptRoot\..\lib\logging.ps1"
+. "$PSScriptRoot\..\lib\path.ps1"
+. "$PSScriptRoot\..\..\lib\Read-ToolVersion.ps1"
+
+function Install-Lazygit {
+    $LgVersion = Get-ToolVersion -Name 'lazygit'
+
+    # Detect installed version
+    $InstalledVersion = ''
+    if (Get-Command lazygit -ErrorAction SilentlyContinue) {
+        $raw = (lazygit --version 2>&1) | Select-Object -First 1 | Out-String
+        $m = [regex]::Match($raw, '[0-9]+\.[0-9]+\.[0-9]+')
+        if ($m.Success) { $InstalledVersion = $m.Value }
+    }
+
+    if ($InstalledVersion -eq $LgVersion) {
+        Write-Ok "lazygit already at pinned version $LgVersion"
+        return
+    }
+
+    if ($InstalledVersion) {
+        Write-Info "lazygit $InstalledVersion installed; upgrading to pinned $LgVersion..."
+    } else {
+        Write-Info "Installing lazygit $LgVersion..."
+    }
+
+    # winget preferred; fall back to scoop if winget is unavailable
+    if (Get-Command winget -ErrorAction SilentlyContinue) {
+        winget install --id JesseDuffield.lazygit --version $LgVersion --silent `
+            --accept-source-agreements --accept-package-agreements
+        Assert-LastExit -ToolName "lazygit" -AllowedExitCodes @(0, -1978335189)
+        Refresh-SessionPath
+        Write-Ok "lazygit installed via winget at $LgVersion"
+    } elseif (Get-Command scoop -ErrorAction SilentlyContinue) {
+        Write-Info "winget not available; falling back to scoop..."
+        scoop install lazygit
+        Assert-LastExit -ToolName "lazygit (scoop)"
+        Write-Warn "scoop installed latest lazygit; version may differ from pinned $LgVersion"
+    } else {
+        Write-Err "Neither winget nor scoop available; cannot install lazygit"
+        throw "lazygit install failed: no supported package manager found"
+    }
+}
diff --git a/tests/fixtures/stub-tools/linux/lazygit.sh b/tests/fixtures/stub-tools/linux/lazygit.sh
new file mode 100644
index 0000000..159cb70
--- /dev/null
+++ b/tests/fixtures/stub-tools/linux/lazygit.sh
@@ -0,0 +1,2 @@
+#!/bin/sh
+echo "lazygit" >> "$RUN_LOG"
diff --git a/tests/fixtures/stub-tools/windows/lazygit.ps1 b/tests/fixtures/stub-tools/windows/lazygit.ps1
new file mode 100644
index 0000000..350414a
--- /dev/null
+++ b/tests/fixtures/stub-tools/windows/lazygit.ps1
@@ -0,0 +1,4 @@
+# stub: lazygit
+param()
+$n = 'lazygit'
+if ($env:RUN_LOG) { Add-Content -Path $env:RUN_LOG -Value $n }
diff --git a/tests/test_lazygit_installer.sh b/tests/test_lazygit_installer.sh
new file mode 100644
index 0000000..d2f74af
--- /dev/null
+++ b/tests/test_lazygit_installer.sh
@@ -0,0 +1,109 @@
+#!/usr/bin/env bash
+# tests/test_lazygit_installer.sh -- parity tests for lazygit opt-in installer (#467)
+#
+# Tests:
+#   T_lazygit_in_list      -- lazygit appears in --list output (opt-in discoverable)
+#   T_lazygit_not_default  -- lazygit is NOT installed by a default no-arg run
+#   T_lazygit_version_pin  -- .tool-versions contains a lazygit pin
+#   T_lazygit_optin_stub   -- --only=lazygit with stub dir runs only lazygit
+#
+# Usage: bash tests/test_lazygit_installer.sh
+# Requires: bash 3.2+ (macOS compatible)
+
+set -uo pipefail
+
+PASS=0
+FAIL=0
+SKIP=0
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[0;33m'
+RESET='\033[0m'
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "${SCRIPT_DIR}/.." && pwd)"
+LINUX_SETUP="${REPO_ROOT}/scripts/linux/setup.sh"
+TOOL_VERSIONS="${REPO_ROOT}/.tool-versions"
+STUB_DIR="${REPO_ROOT}/tests/fixtures/stub-tools/linux"
+
+pass() { printf "${GREEN}PASS${RESET}: %s\n" "$1"; PASS=$((PASS + 1)); }
+fail() { printf "${RED}FAIL${RESET}: %s\n" "$1"; FAIL=$((FAIL + 1)); }
+# shellcheck disable=SC2329
+skip() { printf "${YELLOW}SKIP${RESET}: %s -- %s\n" "$1" "$2"; SKIP=$((SKIP + 1)); }
+
+# ---------------------------------------------------------------------------
+# T_lazygit_in_list: --list on real tools dir includes 'lazygit'
+# Fails RED when scripts/linux/tools/lazygit.sh does not exist.
+# ---------------------------------------------------------------------------
+echo ""
+echo "--- T_lazygit_in_list ---"
+list_out="$(bash "$LINUX_SETUP" --list 2>&1)" && list_exit=$? || list_exit=$?
+if [ "$list_exit" -ne 0 ]; then
+  fail "T_lazygit_in_list: --list exited $list_exit (expected 0)"
+elif echo "$list_out" | grep -qF "lazygit"; then
+  pass "T_lazygit_in_list: lazygit appears in --list output (opt-in discoverable)"
+else
+  fail "T_lazygit_in_list: lazygit missing from --list output (is lazygit.sh in tools/?)"
+  echo "  --list output: $list_out"
+fi
+
+# ---------------------------------------------------------------------------
+# T_lazygit_not_default: default no-arg run with stub dir does NOT run lazygit
+# lazygit is opt-in; it must not appear in defaults.txt.
+# ---------------------------------------------------------------------------
+echo ""
+echo "--- T_lazygit_not_default ---"
+RUN_LOG="$(mktemp)"
+export RUN_LOG
+bash "$LINUX_SETUP" "--tools-dir=${STUB_DIR}" >/dev/null 2>&1 || true
+if grep -qF "lazygit" "$RUN_LOG" 2>/dev/null; then
+  fail "T_lazygit_not_default: lazygit ran in a default no-arg install (must be opt-in only)"
+else
+  pass "T_lazygit_not_default: lazygit does NOT run in a default install (correctly opt-in)"
+fi
+rm -f "$RUN_LOG"
+unset RUN_LOG
+
+# ---------------------------------------------------------------------------
+# T_lazygit_version_pin: .tool-versions contains a lazygit entry
+# Fails RED before lazygit is added to .tool-versions.
+# ---------------------------------------------------------------------------
+echo ""
+echo "--- T_lazygit_version_pin ---"
+if grep -qE '^lazygit[[:space:]]' "$TOOL_VERSIONS" 2>/dev/null; then
+  ver="$(grep -E '^lazygit[[:space:]]' "$TOOL_VERSIONS" | awk '{print $2}')"
+  pass "T_lazygit_version_pin: lazygit pinned at ${ver} in .tool-versions"
+else
+  fail "T_lazygit_version_pin: lazygit not found in .tool-versions -- RED (pre-implementation)"
+fi
+
+# ---------------------------------------------------------------------------
+# T_lazygit_optin_stub: --only=lazygit with stub dir runs only lazygit
+# Fails RED when tests/fixtures/stub-tools/linux/lazygit.sh does not exist.
+# ---------------------------------------------------------------------------
+echo ""
+echo "--- T_lazygit_optin_stub ---"
+RUN_LOG2="$(mktemp)"
+export RUN_LOG
+RUN_LOG="$RUN_LOG2"
+bash "$LINUX_SETUP" "--tools-dir=${STUB_DIR}" --only=lazygit 2>&1 | grep -q . || true
+if grep -qF "lazygit" "$RUN_LOG2" 2>/dev/null; then
+  actual="$(cat "$RUN_LOG2")"
+  if [ "$actual" = "lazygit" ]; then
+    pass "T_lazygit_optin_stub: --only=lazygit runs only lazygit via stub"
+  else
+    fail "T_lazygit_optin_stub: --only=lazygit ran unexpected tools: ${actual}"
+  fi
+else
+  fail "T_lazygit_optin_stub: --only=lazygit did not run lazygit (stub missing or tool unregistered)"
+fi
+rm -f "$RUN_LOG2"
+unset RUN_LOG
+
+# ---------------------------------------------------------------------------
+echo ""
+echo "Results: ${PASS} passed, ${FAIL} failed, ${SKIP} skipped"
+if [ "$FAIL" -gt 0 ]; then
+  exit 1
+fi
+exit 0
diff --git a/tests/test_lazygit_installer_pwsh.ps1 b/tests/test_lazygit_installer_pwsh.ps1
new file mode 100644
index 0000000..1d74dc9
--- /dev/null
+++ b/tests/test_lazygit_installer_pwsh.ps1
@@ -0,0 +1,116 @@
+# tests/test_lazygit_installer_pwsh.ps1 -- parity tests for lazygit opt-in installer (#467)
+#
+# Tests:
+#   T_lazygit_in_list     -- lazygit appears in -List output (opt-in discoverable)
+#   T_lazygit_not_default -- lazygit is NOT installed by a default no-arg run
+#   T_lazygit_version_pin -- .tool-versions contains a lazygit pin
+#   T_lazygit_optin_stub  -- -Only 'lazygit' with stub dir runs only lazygit
+#
+# Usage: powershell -ExecutionPolicy Bypass -File tests\test_lazygit_installer_pwsh.ps1
+# PS 5.1 ASCII-only: no smart quotes, em-dashes, or non-ASCII characters.
+
+$ErrorActionPreference = 'Stop'
+$TestsPassed  = 0
+$TestsFailed  = 0
+$TestsSkipped = 0
+
+$RepoRoot    = Split-Path $PSScriptRoot -Parent
+$WinSetup    = Join-Path $RepoRoot 'scripts\windows\setup.ps1'
+$StubDir     = Join-Path $RepoRoot 'tests\fixtures\stub-tools\windows'
+$ToolVersions = Join-Path $RepoRoot '.tool-versions'
+
+function Test-Scenario {
+    param([string]$Name, [scriptblock]$Test)
+    Write-Host "`n=== TEST: $Name ===" -ForegroundColor Cyan
+    try {
+        & $Test
+        Write-Host "[PASS] $Name" -ForegroundColor Green
+        $script:TestsPassed++
+    }
+    catch {
+        Write-Host "[FAIL] $Name" -ForegroundColor Red
+        Write-Host "  Error: $_" -ForegroundColor Red
+        $script:TestsFailed++
+    }
+}
+
+# ---------------------------------------------------------------------------
+# T_lazygit_in_list: -List on real registry includes 'lazygit'
+# Fails RED when lazygit.ps1 is not dot-sourced + registered in setup.ps1.
+# ---------------------------------------------------------------------------
+
+Test-Scenario "T_lazygit_in_list: lazygit appears in -List output (opt-in discoverable)" {
+    $out = powershell -NoProfile -ExecutionPolicy Bypass -File $WinSetup -List 2>&1 | Out-String
+    $ec  = $LASTEXITCODE
+    if ($ec -ne 0) { throw "-List exited $ec (expected 0)" }
+    if ($out -notmatch '\blazygit\b') {
+        throw "lazygit missing from -List output; has lazygit.ps1 been registered in ToolRegistry?"
+    }
+}
+
+# ---------------------------------------------------------------------------
+# T_lazygit_not_default: default no-arg run with stub dir does NOT run lazygit
+# ---------------------------------------------------------------------------
+
+Test-Scenario "T_lazygit_not_default: lazygit does NOT run in a default install (opt-in only)" {
+    $runLog = [System.IO.Path]::GetTempFileName()
+    $env:RUN_LOG = $runLog
+    try {
+        powershell -NoProfile -ExecutionPolicy Bypass -File $WinSetup `
+            -ToolsDir $StubDir 2>&1 | Out-Null
+        $content = Get-Content $runLog -ErrorAction SilentlyContinue
+        if ($content -contains 'lazygit') {
+            throw "lazygit ran in a default no-arg install (must be opt-in only)"
+        }
+    }
+    finally {
+        $env:RUN_LOG = $null
+        Remove-Item $runLog -ErrorAction SilentlyContinue
+    }
+}
+
+# ---------------------------------------------------------------------------
+# T_lazygit_version_pin: .tool-versions contains a lazygit entry
+# Fails RED before lazygit is added to .tool-versions.
+# ---------------------------------------------------------------------------
+
+Test-Scenario "T_lazygit_version_pin: lazygit is pinned in .tool-versions" {
+    $lines = Get-Content $ToolVersions
+    $entry = $lines | Where-Object { $_ -match '^lazygit\s+' }
+    if (-not $entry) {
+        throw "lazygit not found in .tool-versions -- RED (pre-implementation)"
+    }
+    $ver = ($entry -split '\s+')[1]
+    Write-Host "  lazygit pinned at $ver" -ForegroundColor DarkGray
+}
+
+# ---------------------------------------------------------------------------
+# T_lazygit_optin_stub: -Only 'lazygit' with stub dir runs only lazygit
+# Fails RED when lazygit.ps1 stub is not in the stub dir OR not in ToolRegistry.
+# ---------------------------------------------------------------------------
+
+Test-Scenario "T_lazygit_optin_stub: -Only 'lazygit' runs only lazygit via stub" {
+    $runLog = [System.IO.Path]::GetTempFileName()
+    $env:RUN_LOG = $runLog
+    try {
+        powershell -NoProfile -ExecutionPolicy Bypass -File $WinSetup `
+            -ToolsDir $StubDir -Only 'lazygit' 2>&1 | Out-Null
+        $content = Get-Content $runLog -ErrorAction SilentlyContinue
+        if (-not $content) { throw "-Only 'lazygit' produced empty run-log" }
+        if ($content -notcontains 'lazygit') {
+            throw "-Only 'lazygit' did not run lazygit stub; log: $($content -join ', ')"
+        }
+        $extra = $content | Where-Object { $_ -ne 'lazygit' }
+        if ($extra) { throw "-Only 'lazygit' ran unexpected tools: $($extra -join ', ')" }
+    }
+    finally {
+        $env:RUN_LOG = $null
+        Remove-Item $runLog -ErrorAction SilentlyContinue
+    }
+}
+
+# ---------------------------------------------------------------------------
+Write-Host ""
+Write-Host "Results: $TestsPassed passed, $TestsFailed failed, $TestsSkipped skipped"
+if ($TestsFailed -gt 0) { exit 1 }
+exit 0