diff --git a/src/extension.ts b/src/extension.ts
index 5a88690..ad88dfd 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -8,7 +8,7 @@ import { runCommand } from './util/scripts';
 import { looksLikePath, resolvePath, findWorkspaceRoot } from './util/path';
 import { diagnosticsUnion } from './util/diagnostics';
 import { CodeActionProvider } from './util/codeActions';
-import { writeSuppressionToProjectFile } from './util/files';
+import { parseSuppressionsFromProjectFile, writeSuppressionToProjectFile } from './util/files';
 
 // To keep track of document changes we save hashed versions of their content to this record
 let documentHashMemory : Record<string, string> = {};
@@ -466,12 +466,16 @@ async function runCppcheckOnFileXML(
     let usingProjectFile = false;
     cppcheckProjectFileUri = undefined;
 
-    const args = [
+    // Cast to Set and back to array to filter out duplicate arguments
+    const args = [...new Set([
         '--enable=all',
         '--inline-suppr',
         '--xml',
+        '--suppress=unusedFunction',
+        '--suppress=missingInclude',
+        '--suppress=missingIncludeSystem',
         ...argsParsed,
-    ].filter(Boolean);
+    ])].filter(Boolean);
 
     if (processedArgs.includes("--project=")) {
         usingProjectFile = true;
@@ -481,12 +485,16 @@ async function runCppcheckOnFileXML(
         var projectFileType = projectFilePath.split('.')[1];
         if (projectFileType.toLowerCase() === 'cppcheck') {
             cppcheckProjectFileUri = vscode.Uri.file(projectFilePath);
+            // Duplicate suppressions returns an error from cppcheck, so for ease of use we filter these out
+            const projectFileSuppressions = await parseSuppressionsFromProjectFile(cppcheckProjectFileUri);
+            for (const projectFileSuppression of projectFileSuppressions) {
+                const duplicateSuppressionIndex = args.findIndex((a) => a === `--suppress=${projectFileSuppression}`);
+                if (duplicateSuppressionIndex !== -1) {
+                    args.splice(duplicateSuppressionIndex, 1);
+                }
+            }
         }
     } else {
-        args.push(
-        '--suppress=unusedFunction',
-        '--suppress=missingInclude',
-        '--suppress=missingIncludeSystem');
         args.push(filePath);
     }
 
diff --git a/src/util/files.ts b/src/util/files.ts
index 00e0e2d..ba1e644 100644
--- a/src/util/files.ts
+++ b/src/util/files.ts
@@ -1,5 +1,29 @@
 import * as vscode from 'vscode';
 
+export async function parseSuppressionsFromProjectFile(projectFileUri: vscode.Uri) : Promise<String[]> {
+    const fileType = projectFileUri.toString().split('.')[1];
+    if (fileType !== 'cppcheck') {
+        throw new Error(`Function parseSuppressionsFromProjectFile only supports parsing .cppcheck project files! Recieved file is of type .${fileType}`);
+    }    
+    
+    // Open project file with vscode workspace API
+    const document = await vscode.workspace.openTextDocument(projectFileUri);
+    const text = document.getText();
+
+    // Parse suppression lines and map to an array of error codes, e.g. ['unusedFunction', 'missingInclude']
+    const match = /<suppressions\b[^>]*>([\s\S]*?)<\/suppressions>/m.exec(text);
+    if (!match) {
+        return [];
+    } else {
+           const suppressionsRegex = /<suppression\b[^>]*>([\s\S]*?)<\/suppression>/gm;
+           const suppressions = match[0].matchAll(suppressionsRegex);
+           if (!suppressions) {
+            return [];
+           }
+           return [...suppressions].map(m => m[1]);         
+    }
+}
+
 export async function writeSuppressionToProjectFile(projectFileUri : vscode.Uri, warningType : String) : Promise<boolean> {
     const fileType = projectFileUri.toString().split('.')[1];
     if (fileType !== 'cppcheck') {