After a diagnosis of multiple sclerosis ended his dream of serving as an officer in the United States Navy, Martineau returned to Manchester where he taught Physical Education and American History at his old junior high school.
In 2006, Martineau was elected to the New Hampshire General Court representing Manchester's Ward 9.
After being admitted to the New Hampshire Bar Association as well as the Massachusetts Bar Association, Martineau put his law career on hold to coach women's rugby at St. Anselm College and work in the autism program at Smyth Road School.
On November 8, 2016, he was elected to represent Hillsborough District 42, which consists of Manchester Wards 1, 2, and 3.
He sits on the House Fish and Game and Marine Resources Committee.