Amateur After two years with the
National Team Development Program (USNTDP), Farrell began playing in the
United States Hockey League (USHL) with the
Chicago Steel. He was originally meant to begin his
collegiate career with the
Harvard Crimson during the
2020–21 season, however, following the onset of the
COVID-19 pandemic, all
Ivy League teams opted not to participate in the athletic season. As a result, it was decided that he would return for an additional season in the USHL. The pandemic also resulted in the
2020 NHL entry draft not being held in-person as originally planned, with Farrell and his father watching his draft announcement in a pub at the Steel's
Fox Valley Ice Arena. He later called it "a bright spot in a pretty weird year for everyone." During the
2020–21 season, Farrell recorded 29 goals and 72 assists in 53 games for the Steel, becoming the second player in USHL history to surpass 100 points in a season, after
Kevin Roy in
2012. Following an outstanding campaign, he was awarded both the
USHL Player of the Year and
Dave Tyler Junior Player of the Year Award.
Collegiate Farrell belatedly began his
National Collegiate Athletic Association (NCAA) career for the Crimson during the
2021–22 NCAA season. During
his sophomore year, he led the conference in goals (17), assists (19), and points (36). He finished fourth in the conference with three game-winners and third with 77 shots through 22 games. Following an outstanding season he was named to the
All-ECAC Hockey First Team and the
ECAC Hockey Player of the Year.
Professional Selected in the fifth round (124th overall) by the
Montreal Canadiens of the
National Hockey League (NHL) in the
2020 NHL entry draft, Farrell signed a three-year, entry-level contract with the team on March 26, 2023. He made his NHL debut two days later in a game against the
Philadelphia Flyers whereas his first goal came on his first shot in the league in a 5–2 loss to the
Florida Panthers on March 30. After attending the ensuing training camp with the Canadiens that September, Farrell would be assigned to Montreal's
American Hockey League (AHL) affiliate, the
Laval Rocket, to start the
2023–24 season. On February 7, 2025, he registered his first professional
hat-trick in a game versus the
Toronto Marlies. Entering the offseason as a
restricted free agent, Farrell was extended a qualifying offer by the Canadiens on June 30, 2025. Two days later, he would agree to a one-year extension with the organization. ==International play==