Overview
No. You cannot link two separate GitHub accounts to a single CircleCI account, and you cannot merge two GitHub identities into one CircleCI user.
The same rule applies to Bitbucket: one connected account per VCS provider on a given CircleCI account.
What you can do instead
Goal | What to do |
Use GitHub and Bitbucket (or GitLab) on the same CircleCI user | Connect each provider once under User Settings → Account Integrations |
Access more than one GitHub organization | Stay on one GitHub user that is a member of those orgs, or connect additional orgs from the org switcher |
Consolidate two CircleCI logins |
If your GitHub user is already tied to another CircleCI account, connecting it again fails with an identity-already-associated error. In that case, free the VCS connection from the other account first. See How to Manage Your VCS Connections with CircleCI and delete your user identity.