Search all branches created by a user in a GitHub repository

This is for OS X. Just adding grep on to this answer here and modifying for email, you get

git for-each-ref --format='%(committerdate) %09 %(authoremail) %09 %(refname)' | sort -k5n -k2M -k3n -k4n | grep <author-email>

which works quite well.

[Other answer did not work for me, not sure why]

Loop on the branch, display the last commit information, and grep on the username.

You will have the commit id you are looking for:

for co in `git branch -a --no-merge`; do  git log -1 --no-walk --pretty=format:"%h - %an, %ar : %s" $co; done | grep <knownUserName>