So the steps to delete gmail account permanently are:
1. Sign Out of All Your Google Accounts.Make sure that you are signed out of all your multiple accounts that you are using on Google website. Check for that you are signed out of Gmail, Google+,Youtube and Google Drive.2. Log In to the Google Account that you want to Delete. Look on the top-right corner and Click on Sign In Button.
3. Open Your Account Details. Click on your Profile Pic and then click on Account.
4.Click on Data Tools.
5.In the Data Tools, click on Delete Account and Data.
6. Check all the boxes. Make sure that you have checked all the boxes as it is important to check all the boxes to Delete your Gmail Account.
7. Close Your Account. Enter Your Account Password and then check the boxes that follows to confirm that you want to delete your Google Account, then click on Delete Google Account.
Now, your Google Account has been Deleted Permanently.
Hope, you enjoyed this tutorial.