John was born the fourth of seven children of Philip and Loretta Keenan. His father worked in the mailing room of the Record American, and then the Boston Herald, while his mother worked at Filene’s department store and then CNA Insurance. John was raised in Quincy and attended the Quincy Public Schools, graduating in 1982 from North Quincy High School. He went to Harvard University, earning his way through by working in the athletic department equipment room. He also worked the Saturday overnight shift at the Herald. John graduated with honors from Harvard in 1986, with a government concentration. Three years later, he graduated from Suffolk University Law School. A lifelong learner, in May 2019 John graduated from the Harvard Kennedy School with a Masters in Public Administration.

After law school, John worked first as a litigator, then as a public defender, followed by work as an attorney combating insurance fraud. He is admitted to practice in all Massachusetts State Courts, the Federal District Court for the District of Massachusetts, the Federal First Circuit Court of Appeals, and the United States Supreme Court.

While in law school, John was appointed to serve as the Chairperson of the Quincy Mayor’s Commission on Handicapped Affairs, and was then appointed to the Quincy Zoning Board of Appeals, on which he served for seven years. In 1997 he was appointed Executive Secretary in the administration of Quincy Mayor Jim Sheets. As Executive Secretary he managed 22 municipal department heads and was responsible for the preparation and presentation of Quincy’s budget and the review of all financial matters. In 2001, John became Executive Director of the Norfolk County Retirement System, a public pension system with approximately 10,000 active and retired members, and assets of over $500 million.

While serving as Executive Director of the Norfolk County Retirement System, in 2003 John was appointed to the Quincy City Council to fill a vacant seat, and was elected Councilor at Large in 2004. He served as Chairman of the Council’s Finance Committee for eight years, and in 2010 was elected to the State Senate, Norfolk and Plymouth district. He finished the final year of his term on the Quincy City Council while beginning his term in the State Senate.

Since being elected to the Senate, John has served as the Senate Chair of the Joint Committee on Mental Health and Substance Abuse, the Senate Chair of the Joint Committee on Public Health, the Chair of the Senate Committee on Bonding, Capital Expenditures and State Assets, and the Chair of the Senate Committee on Post Audit and Oversight. Now in his sixth term, John currently serves as the Chair of the Joint Committee on Housing and Chair of the Senate Committee on Intergovernmental Affairs. 

John resides at 37 Hobomack Road with his wife Jeanne Hopkins, and their three children. He is a member of the Merrymount Association, the Ward One Democratic Committee, the Quincy City Club, Friends of the Thomas Crane Public Library, and the Harvard Club of Quincy. He has also coached in the Sacred Heart Youth Basketball Program.