diff --git a/common/changes/@microsoft/rush/fix-rush-list-json-stderr_2026-05-17-19-00.json b/common/changes/@microsoft/rush/fix-rush-list-json-stderr_2026-05-17-19-00.json
new file mode 100644
index 0000000000..131d6335a6
--- /dev/null
+++ b/common/changes/@microsoft/rush/fix-rush-list-json-stderr_2026-05-17-19-00.json
@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "comment": "Route the \"Lockfile was created or deleted\" warning to stderr so that machine-readable output (e.g. `rush list --json`) remains parseable when the lockfile was added or removed in the diff range.",
+      "type": "patch",
+      "packageName": "@microsoft/rush"
+    }
+  ],
+  "packageName": "@microsoft/rush",
+  "email": "sshaurya914@gmail.com"
+}
diff --git a/libraries/rush-lib/src/logic/ProjectChangeAnalyzer.ts b/libraries/rush-lib/src/logic/ProjectChangeAnalyzer.ts
index 43cd967a9d..236f41285e 100644
--- a/libraries/rush-lib/src/logic/ProjectChangeAnalyzer.ts
+++ b/libraries/rush-lib/src/logic/ProjectChangeAnalyzer.ts
@@ -220,11 +220,13 @@ export class ProjectChangeAnalyzer {
         if (shrinkwrapStatus) {
           if (shrinkwrapStatus.status !== 'M') {
             if (rushConfiguration.subspacesFeatureEnabled) {
-              terminal.writeLine(
+              terminal.writeWarningLine(
                 `"${subspace.subspaceName}" subspace lockfile was created or deleted. Assuming all projects are affected.`
               );
             } else {
-              terminal.writeLine(`Lockfile was created or deleted. Assuming all projects are affected.`);
+              terminal.writeWarningLine(
+                `Lockfile was created or deleted. Assuming all projects are affected.`
+              );
             }
             for (const project of subspaceProjects) {
               changedProjects.add(project);