diff --git a/eng/pipelines/pr-validation-pipeline.yml b/eng/pipelines/pr-validation-pipeline.yml
index 8cc7ea8e..1c0eff72 100644
--- a/eng/pipelines/pr-validation-pipeline.yml
+++ b/eng/pipelines/pr-validation-pipeline.yml
@@ -7,6 +7,27 @@ trigger:
       - main
 
 jobs:
+# Shift-left secret scanning: run the 1ES Secret Scanning (SEC101 / SPMI) engine
+# on every PR so credential leaks (e.g. SEC101/037 SqlLegacyCredentials) are caught
+# pre-merge, instead of surfacing later at the GitHub->ADO sync push-protection gate.
+- job: SecretScan
+  displayName: 'Secret Scan (shift-left SEC101)'
+  pool:
+    vmImage: 'windows-latest'
+  steps:
+  - task: 1ESSecretScanning@1
+    displayName: 'Run 1ES Secret Scanning'
+    inputs:
+      Action: 'analyze'
+      Target: '$(Build.SourcesDirectory)\*'
+      Rules: 'GetClean'
+      Recurse: true
+  - task: PowerShell@2
+    displayName: 'Fail build if secrets detected in shipping source'
+    inputs:
+      filePath: '$(Build.SourcesDirectory)/eng/pipelines/scripts/secretscan-gate.ps1'
+      pwsh: false
+
 - job: CodeQLAnalysis
   displayName: 'CodeQL Security Analysis'
   pool:
diff --git a/eng/pipelines/scripts/secretscan-gate.ps1 b/eng/pipelines/scripts/secretscan-gate.ps1
new file mode 100644
index 00000000..88154932
--- /dev/null
+++ b/eng/pipelines/scripts/secretscan-gate.ps1
@@ -0,0 +1,101 @@
+<#
+.SYNOPSIS
+    Shift-left secret-scan gate. Fails the build when 1ESSecretScanning (SPMI /
+    SEC101) reports a credential leak in shipping source, while allowing the
+    sample credentials that legitimately live in test / benchmark / pipeline dirs.
+
+.DESCRIPTION
+    The 1ESSecretScanning task only emits SARIF *warnings*; on its own it never
+    fails the run, and PostAnalysis@2's break filter does not cover it. This
+    script reads the emitted SARIF, keeps SEC101* findings, drops anything under
+    the paths already excluded by .config/CredScanSuppressions.json, and exits 1
+    if any real finding remains. Path policy is kept in sync with that file.
+#>
+param(
+    [string]$SourcesDir = $env:BUILD_SOURCESDIRECTORY,
+    [string]$SearchRoot = $env:AGENT_BUILDDIRECTORY
+)
+
+$ErrorActionPreference = 'Stop'
+
+# Directories where sample/dummy credentials are allowed (mirror of
+# .config/CredScanSuppressions.json). Matched against repo-relative, '/'-normalized paths.
+$excludedPrefixes = @('tests/', 'benchmarks/', 'eng/', 'OneBranchPipelines/', '.gdn/', '.git/')
+
+# The scanner writes its SARIF under <BuildDir>/.gdn/.r/**. That directory is
+# hidden, so a plain -Recurse would skip it (and could match an unrelated empty
+# SARIF elsewhere) - search the known dir first, with -Force, then fall back.
+$sarifFiles = @()
+$gdnResults = Join-Path $SearchRoot '.gdn/.r'
+if (Test-Path $gdnResults) {
+    $sarifFiles = @(Get-ChildItem -Path $gdnResults -Recurse -Filter '*.sarif' -Force -ErrorAction SilentlyContinue)
+}
+if (-not $sarifFiles) {
+    $sarifFiles = @(Get-ChildItem -Path $SearchRoot -Recurse -Filter '*.sarif' -Force -ErrorAction SilentlyContinue)
+}
+if (-not $sarifFiles) {
+    Write-Host "No SARIF output found under '$SearchRoot' - secret scanner did not produce results."
+    exit 0
+}
+
+Write-Host "Found $($sarifFiles.Count) SARIF file(s):"
+$sarifFiles | ForEach-Object { Write-Host "  $($_.FullName)" }
+
+$srcNorm = ($SourcesDir -replace '\\', '/').TrimEnd('/')
+$violations = New-Object System.Collections.Generic.List[string]
+
+foreach ($file in $sarifFiles) {
+    try {
+        $sarif = Get-Content -LiteralPath $file.FullName -Raw | ConvertFrom-Json
+    } catch {
+        Write-Host "##[warning]Could not parse SARIF '$($file.FullName)': $_"
+        continue
+    }
+
+    foreach ($run in @($sarif.runs)) {
+        $rules = @($run.tool.driver.rules)
+        Write-Host "  $($file.Name): $(@($run.results).Count) result(s), $($rules.Count) rule(s) in driver"
+        foreach ($result in @($run.results)) {
+            # Resolve the rule id across SARIF variants: result.ruleId, result.rule.id,
+            # or result.ruleIndex -> tool.driver.rules[index].id
+            $rid = $result.ruleId
+            if (-not $rid -and $result.rule) { $rid = $result.rule.id }
+            if (($rid -notmatch 'SEC101') -and ($null -ne $result.ruleIndex) -and $rules.Count -gt 0) {
+                $idx = [int]$result.ruleIndex
+                if ($idx -ge 0 -and $idx -lt $rules.Count) { $rid = $rules[$idx].id }
+            }
+            if ($rid -notmatch 'SEC101') { continue }
+
+            foreach ($loc in @($result.locations)) {
+                $uri = $loc.physicalLocation.artifactLocation.uri
+                if (-not $uri) { continue }
+
+                $rel = $uri -replace '^file:///', '' -replace '\\', '/'
+                if ($srcNorm) { $rel = $rel -replace ('^' + [regex]::Escape($srcNorm) + '/'), '' }
+                $rel = $rel.TrimStart('/')
+
+                $skip = $false
+                foreach ($prefix in $excludedPrefixes) {
+                    if ($rel.StartsWith($prefix, [System.StringComparison]::OrdinalIgnoreCase)) { $skip = $true; break }
+                }
+                if ($skip) { continue }
+
+                $line = $loc.physicalLocation.region.startLine
+                $msg = $result.message.text
+                $violations.Add("${rel}:${line}  ${rid}  $msg")
+            }
+        }
+    }
+}
+
+if ($violations.Count -gt 0) {
+    Write-Host "##[error]Secret scan found $($violations.Count) credential leak(s) in shipping source (outside allowed sample paths):"
+    foreach ($v in $violations) { Write-Host "##[error]  $v" }
+    Write-Host ""
+    Write-Host "If a finding is an intentional sample credential, place it under an allowed path"
+    Write-Host "(tests/, benchmarks/, eng/, OneBranchPipelines/) or add a Guardian baseline entry."
+    exit 1
+}
+
+Write-Host "Secret scan gate passed: no SEC101 findings in shipping source."
+exit 0