Gallivan got his start improvising in his hometown of Boston as well as performing at the Bambi Masterpiece Theater, before moving to Chicago in 2003, where he performed at
The Second City between 2003 and 2007, appearing in four mainstage revues, including the long-running
Between Barack and a Hard Place. He was twice nominated for
Joseph Jefferson Awards for his work while there. Gallivan appeared in the
Matt Damon film
The Informant! and in the
Derek Westerman web series
Bad Dads alongside
Michael Cera. Gallivan appeared in the feature film
A Thousand Words. Gallivan was a writer on the
NBC sitcom
Are You There, Chelsea? and the
ABC comedy series
Happy Endings. For the 2014–15 television season, Gallivan created and produced the
CBS television sitcom
The McCarthys, which was cancelled in early 2015. ==Personal life==