diff --git a/lib/entry-points.js b/lib/entry-points.js
index 0e179f3fc7..7bee9b2bb7 100644
--- a/lib/entry-points.js
+++ b/lib/entry-points.js
@@ -186700,6 +186700,7 @@ async function uploadBundledDatabase(repositoryNwo, language, commitOid, bundled
 var upload_lib_exports = {};
 __export(upload_lib_exports, {
   buildPayload: () => buildPayload,
+  countResultsInSarif: () => countResultsInSarif,
   filterAlertsByDiffRange: () => filterAlertsByDiffRange,
   findSarifFilesInDir: () => findSarifFilesInDir,
   getGroupedSarifFilePaths: () => getGroupedSarifFilePaths,
@@ -188393,11 +188394,10 @@ async function getGroupedSarifFilePaths(logger2, sarifPath) {
 }
 function countResultsInSarif(sarifLog) {
   let numResults = 0;
-  const parsedSarif = JSON.parse(sarifLog);
-  if (!Array.isArray(parsedSarif.runs)) {
+  if (!Array.isArray(sarifLog.runs)) {
     throw new InvalidSarifUploadError("Invalid SARIF. Missing 'runs' array.");
   }
-  for (const run9 of parsedSarif.runs) {
+  for (const run9 of sarifLog.runs) {
     if (!Array.isArray(run9.results)) {
       throw new InvalidSarifUploadError(
         "Invalid SARIF. Missing 'results' array in run."
@@ -188598,7 +188598,7 @@ async function uploadPostProcessedFiles(logger2, checkoutPath, uploadTarget, pos
   logger2.debug(`Raw upload size: ${rawUploadSizeBytes} bytes`);
   const zippedUploadSizeBytes = zippedSarif.length;
   logger2.debug(`Base64 zipped upload size: ${zippedUploadSizeBytes} bytes`);
-  const numResultInSarif = countResultsInSarif(sarifPayload);
+  const numResultInSarif = countResultsInSarif(sarifLog);
   logger2.debug(`Number of results in upload: ${numResultInSarif}`);
   const sarifID = await uploadPayload(
     payload,
diff --git a/src/upload-lib.test.ts b/src/upload-lib.test.ts
index 4738c07c62..df7f00d9ec 100644
--- a/src/upload-lib.test.ts
+++ b/src/upload-lib.test.ts
@@ -24,6 +24,50 @@ test.beforeEach(() => {
   getEnv().initialise("1.2.3");
 });
 
+test.serial(
+  "countResultsInSarif counts materialized results across runs",
+  (t) => {
+    const tool = { driver: { name: "test" } };
+    const result = { message: { text: "Finding" } };
+    t.is(uploadLib.countResultsInSarif({ runs: [] }), 0);
+    t.is(
+      uploadLib.countResultsInSarif({
+        runs: [
+          { tool, results: [] },
+          { tool, results: [result, result] },
+          { tool, results: [result] },
+        ],
+      }),
+      3,
+    );
+  },
+);
+
+test.serial("countResultsInSarif preserves malformed array errors", (t) => {
+  for (const value of ["{}", '{"runs":null}', '{"runs":{}}']) {
+    t.throws(
+      () =>
+        uploadLib.countResultsInSarif(JSON.parse(value) as Partial<sarif.Log>),
+      {
+        message: "Invalid SARIF. Missing 'runs' array.",
+      },
+    );
+  }
+  for (const value of [
+    '{"runs":[{}]}',
+    '{"runs":[{"results":null}]}',
+    '{"runs":[{"results":{}}]}',
+  ]) {
+    t.throws(
+      () =>
+        uploadLib.countResultsInSarif(JSON.parse(value) as Partial<sarif.Log>),
+      {
+        message: "Invalid SARIF. Missing 'results' array in run.",
+      },
+    );
+  }
+});
+
 test.serial("validateSarifFileSchema - valid", (t) => {
   const inputFile = `${__dirname}/../src/testdata/valid-sarif.sarif`;
   t.notThrows(() =>
diff --git a/src/upload-lib.ts b/src/upload-lib.ts
index 4e97c1d1db..d3e3645dd2 100644
--- a/src/upload-lib.ts
+++ b/src/upload-lib.ts
@@ -425,15 +425,14 @@ export async function getGroupedSarifFilePaths(
   return results;
 }
 
-// Counts the number of results in the given SARIF file
-function countResultsInSarif(sarifLog: string): number {
+// Counts the number of results in the given SARIF object.
+export function countResultsInSarif(sarifLog: Partial<sarif.Log>): number {
   let numResults = 0;
-  const parsedSarif = JSON.parse(sarifLog);
-  if (!Array.isArray(parsedSarif.runs)) {
+  if (!Array.isArray(sarifLog.runs)) {
     throw new InvalidSarifUploadError("Invalid SARIF. Missing 'runs' array.");
   }
 
-  for (const run of parsedSarif.runs) {
+  for (const run of sarifLog.runs) {
     if (!Array.isArray(run.results)) {
       throw new InvalidSarifUploadError(
         "Invalid SARIF. Missing 'results' array in run.",
@@ -799,7 +798,7 @@ export async function uploadPostProcessedFiles(
   logger.debug(`Raw upload size: ${rawUploadSizeBytes} bytes`);
   const zippedUploadSizeBytes = zippedSarif.length;
   logger.debug(`Base64 zipped upload size: ${zippedUploadSizeBytes} bytes`);
-  const numResultInSarif = countResultsInSarif(sarifPayload);
+  const numResultInSarif = countResultsInSarif(sarifLog);
   logger.debug(`Number of results in upload: ${numResultInSarif}`);
 
   // Make the upload
diff --git a/unreleased-change-notes/count-materialized-sarif-results.md b/unreleased-change-notes/count-materialized-sarif-results.md
new file mode 100644
index 0000000000..411c83db6f
--- /dev/null
+++ b/unreleased-change-notes/count-materialized-sarif-results.md
@@ -0,0 +1 @@
+- Reduced SARIF upload postprocessing overhead by counting results directly from the existing SARIF object instead of parsing the serialized payload again.