Kelly appeared on The Daily Show in a correspondent piece by Ed Helms titled "The Clash" in which he criticized Michale Graves for being a Republican.

Kelly (along with Chris McCaughan, co-vocalist of the Lawrence Arms) also provided back-up vocals on Common Rider's This is Unity Music album.

In 2010, Kelly released a split album with Joe McMahon of punk rock band Smoke or Fire, titled Wasted Potential.

Kelly's half of the split contained acoustic versions of Lawrence Arms songs (both his and McCaughan), as well as a cover of "Kiss the Bottle" by Jawbreaker.

During the periods of inactivity of his musical projects, Brendan has been joined by fellow punk rock singers Laura Jane Grace and Brian Fallon in maintaining a blog, Bad Sandwich Chronicles.