People with admin permissions in a repository can permanently delete an issue from a repository.
/articles/deleting-an-issue
free-pro-team
enterprise-server
github-ae
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pull requests
You can only delete issues in a repository owned by your user account. You cannot delete issues in a repository owned by another user account, even if you are a collaborator there.
Collaborators do not receive a notification when you delete an issue. When visiting the URL of a deleted issue, collaborators will see a message stating that the issue is deleted. People with admin or owner permissions in the repository will additionally see the username of the person who deleted the issue and when it was deleted.
Navigate to the issue you want to delete.
On the right side bar, under "Notifications", click Delete issue.