Robert O'Leary has represented Cape Cod, Martha's Vineyard, and Nantucket in the Massachusetts State Senate since his election in 2000. He was the first Democrat elected to represent the Cape and Islands in the State Senate since the end of the Civil War. Prior to his election to the State Legislature, he served as a Barnstable County Commissioner from 1987 through 2001. In addition to being a Senator he is also a tenured professor of history and politics at the Massachusetts Maritime Academy where he has taught for nearly thirty years and at Cape Cod Community College where he is an adjunct professor. 

Senator O'Leary grew up in Lowell and moved to the Cape in the early 1970s and now resides in Cummaquid, a village in the Town of Barnstable. 

He graduated from Kimball Union Academy in New Hampshire, and subsequently earned a Bachelor of Science degree from Georgetown University, a Masters in Public Administration from Harvard University, and a PhD in History from Tufts University. He is the father of three daughters and has four grandchildren. 

Senator O'Leary represents the Cape and Islands District, consisting of the Towns of Barnstable (Precincts 1 through 9 inclusive and precinct 13), Brewster, Chatham, Dennis, Eastham, Harwich, Mashpee, Orleans, Provincetown, Truro, Wellfleet and Yarmouth in the county of Barnstable; Aquinnah, Chilmark, Edgartown, Gosnold, Oak Bluffs, Tisbury, and West Tisbury in the county of Dukes; and Nantucket in the county of Nantucket. 

Senator O'Leary is the Senate Chairman of the Joint Committee on Education and the Senate Vice-Chairman of the Joint Committee on State Administration & Regulatory Oversight. In addition, he also serves on many other committees and boards including: the Joint Committee on Environment, Natural Resources & Agriculture, the Committee on Labor and Workforce Development, the Joint Committee on Community Development & Small Business, the Joint Committee on Mental Health & Substance Abuse and the Senate Committee on Federal Stimulus Oversight.