John Massy succeeded his brother as Baron in 1874. He served as a Representative Peer, a Deputy Lieutenant, and Justice of the Peace for counties Leitrim and Limerick in Ireland, as well as acting as High Sheriff for Leitrim in 1863 and for Limerick in 1873. On 19 March 1863, he married Lady Lucy Maria Butler [d. 1896], daughter of the third Earl of Carrick. They had two daughters (Lucy Matilda Anne and Matilda Isabella) and a son, Hugh Somerset John, who succeeded his father as 7th Baron Massy.