diff --git a/crates/ruff/tests/lint.rs b/crates/ruff/tests/lint.rs
index 579d185d53..01e9bc4583 100644
--- a/crates/ruff/tests/lint.rs
+++ b/crates/ruff/tests/lint.rs
@@ -933,3 +933,42 @@ include = ["*.ipy"]
 
     Ok(())
 }
+
+#[test]
+fn file_noqa_external() -> Result<()> {
+    let tempdir = TempDir::new()?;
+    let ruff_toml = tempdir.path().join("ruff.toml");
+    fs::write(
+        &ruff_toml,
+        r#"
+[lint]
+external = ["AAA"]
+"#,
+    )?;
+
+    insta::with_settings!({
+        filters => vec![(tempdir_filter(&tempdir).as_str(), "[TMP]/")]
+    }, {
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .args(STDIN_BASE_OPTIONS)
+        .arg("--config")
+        .arg(&ruff_toml)
+        .arg("-")
+        .pass_stdin(r#"
+# flake8: noqa: AAA101, BBB102
+import os
+"#), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    -:3:8: F401 [*] `os` imported but unused
+    Found 1 error.
+    [*] 1 fixable with the `--fix` option.
+
+    ----- stderr -----
+    warning: Invalid rule code provided to `# ruff: noqa` at -:2: BBB102
+    "###);
+    });
+
+    Ok(())
+}
diff --git a/crates/ruff_linter/src/checkers/noqa.rs b/crates/ruff_linter/src/checkers/noqa.rs
index 8e01d671ce..58a1efed90 100644
--- a/crates/ruff_linter/src/checkers/noqa.rs
+++ b/crates/ruff_linter/src/checkers/noqa.rs
@@ -29,7 +29,13 @@ pub(crate) fn check_noqa(
     settings: &LinterSettings,
 ) -> Vec<usize> {
     // Identify any codes that are globally exempted (within the current file).
-    let exemption = FileExemption::try_extract(locator.contents(), comment_ranges, path, locator);
+    let exemption = FileExemption::try_extract(
+        locator.contents(),
+        comment_ranges,
+        &settings.external,
+        path,
+        locator,
+    );
 
     // Extract all `noqa` directives.
     let mut noqa_directives = NoqaDirectives::from_commented_ranges(comment_ranges, path, locator);
diff --git a/crates/ruff_linter/src/linter.rs b/crates/ruff_linter/src/linter.rs
index e5a4287f67..66f98ef3bf 100644
--- a/crates/ruff_linter/src/linter.rs
+++ b/crates/ruff_linter/src/linter.rs
@@ -407,6 +407,7 @@ pub fn add_noqa_to_path(
         &diagnostics.0,
         &locator,
         indexer.comment_ranges(),
+        &settings.external,
         &directives.noqa_line_for,
         stylist.line_ending(),
     )
diff --git a/crates/ruff_linter/src/noqa.rs b/crates/ruff_linter/src/noqa.rs
index e98f33bcf7..d50c3b1757 100644
--- a/crates/ruff_linter/src/noqa.rs
+++ b/crates/ruff_linter/src/noqa.rs
@@ -235,6 +235,7 @@ impl FileExemption {
     pub(crate) fn try_extract(
         contents: &str,
         comment_ranges: &CommentRanges,
+        external: &[String],
         path: &Path,
         locator: &Locator,
     ) -> Option<Self> {
@@ -263,6 +264,11 @@ impl FileExemption {
                         }
                         ParsedFileExemption::Codes(codes) => {
                             exempt_codes.extend(codes.into_iter().filter_map(|code| {
+                                // Ignore externally-defined rules.
+                                if external.iter().any(|external| code.starts_with(external)) {
+                                    return None;
+                                }
+
                                 if let Ok(rule) = Rule::from_code(get_redirect_target(code).unwrap_or(code))
                                 {
                                     Some(rule.noqa_code())
@@ -458,6 +464,7 @@ pub(crate) fn add_noqa(
     diagnostics: &[Diagnostic],
     locator: &Locator,
     comment_ranges: &CommentRanges,
+    external: &[String],
     noqa_line_for: &NoqaMapping,
     line_ending: LineEnding,
 ) -> Result<usize> {
@@ -466,6 +473,7 @@ pub(crate) fn add_noqa(
         diagnostics,
         locator,
         comment_ranges,
+        external,
         noqa_line_for,
         line_ending,
     );
@@ -478,6 +486,7 @@ fn add_noqa_inner(
     diagnostics: &[Diagnostic],
     locator: &Locator,
     comment_ranges: &CommentRanges,
+    external: &[String],
     noqa_line_for: &NoqaMapping,
     line_ending: LineEnding,
 ) -> (usize, String) {
@@ -487,7 +496,8 @@ fn add_noqa_inner(
 
     // Whether the file is exempted from all checks.
     // Codes that are globally exempted (within the current file).
-    let exemption = FileExemption::try_extract(locator.contents(), comment_ranges, path, locator);
+    let exemption =
+        FileExemption::try_extract(locator.contents(), comment_ranges, external, path, locator);
     let directives = NoqaDirectives::from_commented_ranges(comment_ranges, path, locator);
 
     // Mark any non-ignored diagnostics.
@@ -1001,6 +1011,7 @@ mod tests {
             &[],
             &Locator::new(contents),
             &CommentRanges::default(),
+            &[],
             &noqa_line_for,
             LineEnding::Lf,
         );
@@ -1021,6 +1032,7 @@ mod tests {
             &diagnostics,
             &Locator::new(contents),
             &CommentRanges::default(),
+            &[],
             &noqa_line_for,
             LineEnding::Lf,
         );
@@ -1048,6 +1060,7 @@ mod tests {
             &diagnostics,
             &Locator::new(contents),
             &comment_ranges,
+            &[],
             &noqa_line_for,
             LineEnding::Lf,
         );
@@ -1075,6 +1088,7 @@ mod tests {
             &diagnostics,
             &Locator::new(contents),
             &comment_ranges,
+            &[],
             &noqa_line_for,
             LineEnding::Lf,
         );