[citation needed] Upon graduation, he decided not to accept offers from technology companies and instead moved to Chicago to work in improvisational comedy.

He then co-founded Burning Door Networked Media, a web design and development consulting company, which was acquired by Digital Knowledge Assets in October 1996.

In 2004, Costolo, along with Eric Lunt, Steve Olechowski, and Matt Shobe, founded the web feed management provider FeedBurner.

[3] On August 8, 2015, The New York Times reported that Costolo would be leaving Twitter's Board of Directors by the end of the year or when a new CEO was appointed.

In December 2015, Costolo announced that he joined the board of directors for Patreon, a startup that helps artists raise money for their creative projects.

In a thread he posted criticizing Coinbase, a cryptocurrency company, and their CEO Brian Armstrong for refusing to participate in certain social and political movements such as Black Lives Matter, Costolo tweeted:[19] Me-first capitalists who think you can separate society from business are going to be the first people lined up against the wall and shot in the revolution.