Cousins played four seasons (2009–2013) of major junior hockey with the Sault Ste. Marie Greyhounds of the Ontario Hockey League, scoring 102 goals and 189 assists for 291 points, while earning 261 penalty minutes in 264 games played. On March 26, 2012, Cousins was signed to a three-year, entry-level contract with the Philadelphia Flyers.[3]
On June 16, 2017, Cousins' five-year tenure with the Flyers ended as he was traded alongside Merrick Madsen to the Arizona Coyotes in exchange for Brendan Warren and a fifth-round choice in the 2018 NHL Entry Draft.[5]
In establishing a bottom-six role, providing an agitating two-way presence within the Coyotes organization, Cousins recorded a career-high 27 points (7 goals, 20 assists), in 81 games in the 2018–19 season. On June 25, 2019, as an impending restricted free agent, Cousins was not tendered a qualifying offer from the Coyotes, releasing him as a free agent.[6]
Montreal Canadiens
On July 5, 2019, Cousins signed a one-year, $1 million contract with the Montreal Canadiens.[7] He skated in 58 games for the club, recording nine goals and 13 assists.
Vegas Golden Knights
On February 24, 2020, Montreal traded Cousins to the Vegas Golden Knights in exchange for a fourth-round selection in the 2021 NHL Entry Draft.[8] Only two weeks after the trade was finalized, the NHL season was suspended indefinitely due to the COVID-19 pandemic. During the pause, Cousins returned to Canada and bonded with his teammates through daily FaceTime calls and other forms of long-distance communication.[9]
Nashville Predators
Leaving the Golden Knights as a free agent, on October 9, 2020, Cousins was signed to a two-year, $3 million contract with the Nashville Predators.[10]
Florida Panthers
Having concluded his contract with the Predators, Cousins joined his sixth NHL club, in signing as a free agent to a two-year, $2.2 million contract with the Florida Panthers on July 13, 2022.[11] On May 12, 2023, He scored the series-winning goal in overtime of game 5 against the Toronto Maple Leafs, sending the Panthers to their first Conference Final since 1996.[12] He won the Stanley Cup in 2024.
Ottawa Senators
After winning the Stanley Cup with the Panthers, Cousins agreed to a one-year, $800,000 contract with the Ottawa Senators on August 29th, 2024.[13]