Lawrence Robert O'Brien (born July 19, 1949) is a Canadian businessman and politician. O'Brien served as the 58th mayor of Ottawa from 2006 until 2010. O'Brien was the founder and former Chair and CEO of Calian Technologies Ltd. O'Brien left Calian as CEO and chairman in 2006 when he was elected mayor of Ottawa. He remained a director of the firm until stepping down in 2012. He ran for re-election in the Ottawa mayoral election in 2010 but was defeated by then former mayor Jim Watson.