Martin O'Malley, a Democrat, served as governor of Maryland from 2007 to 2015. He had earlier served as mayor of Baltimore and on the Baltimore City Council.
O'Malley has staked out liberal stances on a number of issues, including immigration, the death penalty, same-sex marriage and gun control. As governor, he supported the effort to legalize gay marriage in Maryland and also sought to repeal the death penalty.
A lawyer by training, O'Malley got his start in politics with Gary Hart's 1984 presidential bid, working on the campaign's New Hampshire effort.