Cousineau decided to attend Ohio State University, where he played for coach Woody Hayes' Ohio State Buckeyes football team from 1975 to 1978. He was a consensus first-team All-American, and broke a school record with 211 tackles in a single season in 1978. He also broke a school record for most tackles in a game with 29, was the MVP of the Orange Bowl, and remains second on the school's all-time tackles list with 569.
Cousineau was drafted first overall in the 1979 NFL Draft by the Buffalo Bills, who acquired the pick from the San Francisco 49ers in a trade for O.J. Simpson. Cousineau never played a game with the Bills. He instead signed with the Canadian Football LeagueMontreal Alouettes where they offered double the money that the Bills originally offered. Cousineau became a star there, becoming the Grey Cup Most Valuable Player in the 1979 season. Cousineau wanted to return to the NFL, and in 1982 the Houston Oilers attempted to sign him, but the Bills (who still held Cousineau's NFL rights) matched the offer. He was then traded from the Bills to the Cleveland Browns for a first round draft choice (14th overall) in the 1983 NFL Draft. That pick was used on future Hall of Fame quarterback Jim Kelly. Cousineau signed a five-year contract for 2.5 million dollars, the most ever for a Cleveland Brown player at the time.
During Cousineau's four seasons with the Browns, he led the team in tackles for three seasons. He was named a 2nd-team All-NFL by the NEA in 1983, and by the AP in 1984, but never made the Pro Bowl in his career. He was considered an overpaid disappointment in Cleveland, while Bills fans fondly remember the fact that the man who once snubbed them for the CFL was traded for Jim Kelly. Cousineau signed with the San Francisco 49ers as a free agent after the 1985 season where he played two years as a reserve before retiring in 1987.
Cousineau finished his NFL career with ten interceptions and 6.5 career sacks and currently stays at home with his wife, Lisa, and two daughters, Kyle and Kacey, in Akron, Ohio and renovates houses.
St. Edward inducted Cousineau to the school's Athletic Hall of Fame. He married Lisa June 16, 1990, and has 2 daughters Kyle and Kacey. On February 8, 2006, Cousineau announced plans to run for a seat in the Ohio House of Representatives as a Republican in the Akron, Ohio area. He won the May primary but lost the November election to Democrat Brian Williams by a margin of 58% to 42%.