[3] From 2000 to 2005 and again from 2007 to 2008 he practiced law with Kilpatrick Townsend & Stockton in Washington, D.C.[3] From 2005 to 2006 he hosted The Pulse with Corey O'Brien on WOLF-TV in Northeastern Pennsylvania.

In 2011, O'Brien selected Jeanette Mariani, the Mayor of Blakely, as his new running mate after Washo announced his retirement.

In the Democratic primary, O'Brien finished with the second-highest vote total, narrowly ahead of former county chief of staff Elizabeth Randol, but behind the top vote getter, former State Representative James Wansacz.

In the general election, O'Brien and Wansacz received the two highest vote totals, thus continuing the Democratic majority on the board.

From 2010 to 2014 he served as an investor, co-founder, and later managing member of Rapid Recovery in Allentown and Philadelphia.