If the author has a GitHub account, just click the author's username from anywhere in the commit history, and the commits you can see will be filtered down to those by that author:
You can also click the 'n commits' link below their name on the repo's "contributors" page:
Alternatively, you can directly append ?author=<theusername> or ?author=<emailaddress> to the URL. For example, https://github.com/jquery/jquery/commits/master?author=dmethvin or https://github.com/jquery/jquery/commits/[email protected] both give me:
For authors without a GitHub account, only filtering by email address will work, and you will need to manually add ?author=<emailaddress> to the URL - the author's name will not be clickable from the commits list.
You can also get the list of commits by a particular author from the command line using
git log --author=[your git name]
Example:
git log --author=Prem