Mayor Larry O'Brien was born in Ottawa and stayed in Ottawa for his post-secondary education attending Algonquin School of Technology and in 1972 he graduated with a diploma in Technology. Mayor O'Brien has two sons; Michael O'Brien is in third year at the McGill University and Matthew O'Brien lives in Ottawa and attends Appleby College in Oakville.

Mayor O'Brien founded CALIAN Technologies Ltd. in 1982 as a one-person consulting company and was responsible for strategic planning and overall business development. Mr. O'Brien has more than 27 years of business and technical experience and retired as CEO of CALIAN February 2, 2005. The company has grown as a direct result of Larry's strong values; honesty, transparency, value and fiscal prudence.

Mayor O'Brien is a past member of the Prime Minister's Advisory Council on Science and Technology (ACST), a past chairman of the Sectoral Advisory Group on International Trade (SAGIT) on Information Technologies and Telecommunications (IT&T), as well as one the co-chair's of the Regional Economic Diversification Opportunities (REDO) committee. REDO was funded by HRDC in 1996 to assist public servants with their transition into the private sector after Liberal budget cuts and downsizing. Mayor O'Brien also served as chairman of the Canadian Advanced Technology Association (CATA) from 1994 until 1996.

Mayor O'Brien was co-chair of Saint Vincent Hospital's capital campaign in 2004 that successfully achieved its goal of $7.5 million. In 2006 he was awarded the United Way Community builder of the year award. Mr. O'Brien was elected Mayor of the City of Ottawa on November 13, 2006.