diff --git a/src/components/error_boundary/error_boundary.tsx b/src/components/error_boundary/error_boundary.tsx
index 19ee1739870..cb0b3e064b0 100644
--- a/src/components/error_boundary/error_boundary.tsx
+++ b/src/components/error_boundary/error_boundary.tsx
@@ -61,7 +61,8 @@ export class EuiErrorBoundary extends Component<
     // For consistency, rebuild the full error text from the Error subparts.
     const { message, stack } = error;
     const idx = stack?.indexOf(message) || -1;
-    const stackStr = idx > -1 ? stack?.substr(idx + message.length + 1) : stack;
+    const stackStr =
+      idx > -1 ? stack?.substring(idx + message.length + 1) : stack;
     const errorMessage = `Error: ${message}
 ${stackStr}`;
     this.setState({
diff --git a/src/components/highlight/highlight.tsx b/src/components/highlight/highlight.tsx
index 0914ea78e7b..2870b83d1c1 100644
--- a/src/components/highlight/highlight.tsx
+++ b/src/components/highlight/highlight.tsx
@@ -72,7 +72,7 @@ const highlight = (
       <Fragment>
         {chunks.map((chunk) => {
           const { end, highlight, start } = chunk;
-          const value = searchSubject.substr(start, end - start);
+          const value = searchSubject.substring(start, end);
           if (highlight) {
             return (
               <EuiMark
@@ -103,9 +103,12 @@ const highlight = (
     return searchSubject;
   }
 
-  const preMatch: string = searchSubject.substr(0, indexOfMatch);
-  const match: string = searchSubject.substr(indexOfMatch, searchValue.length);
-  const postMatch: string = searchSubject.substr(
+  const preMatch: string = searchSubject.substring(0, indexOfMatch);
+  const match: string = searchSubject.substring(
+    indexOfMatch,
+    indexOfMatch + searchValue.length
+  );
+  const postMatch: string = searchSubject.substring(
     indexOfMatch + searchValue.length
   );
 
diff --git a/src/components/markdown_editor/markdown_editor.tsx b/src/components/markdown_editor/markdown_editor.tsx
index 45551bfcfc1..add06457894 100644
--- a/src/components/markdown_editor/markdown_editor.tsx
+++ b/src/components/markdown_editor/markdown_editor.tsx
@@ -261,8 +261,8 @@ export const EuiMarkdownEditor = forwardRef<
 
     const replaceNode = useCallback(
       (position, next) => {
-        const leading = value.substr(0, position.start.offset);
-        const trailing = value.substr(position.end.offset);
+        const leading = value.substring(0, position.start.offset);
+        const trailing = value.substring(position.end.offset);
         onChange(`${leading}${next}${trailing}`);
       },
       [value, onChange]
diff --git a/upcoming_changelogs/6954.md b/upcoming_changelogs/6954.md
new file mode 100644
index 00000000000..17270a68927
--- /dev/null
+++ b/upcoming_changelogs/6954.md
@@ -0,0 +1,2 @@
+- Updated deprecated `.substr()` usages to `.substring()`
+