Warsofsky had his most productive NHL season in 2017-18, the defenseman's first with the Colorado Avalanche.

Warsofsky went from Cushing Academy in his native Massachusetts to USA Hockey's National Team Development Program in 2007-08 and was named captain. He was captain of the U.S. team that won the bronze medal at the 2008 IIHF World Under-18 Championship. Months later the St. Louis Blues selected him in the fourth round (No. 95) of the 2008 NHL Draft.

He returned to Massachusetts to attend Boston University in 2008 and helped the Terriers win the 2009 NCAA championship. Warsofsky had another solid season at BU in 2009-10, and also helped the U.S. win the gold medal at the 2010 IIHF World Junior Championship.

The Blues traded him to the Boston Bruins on June 26, 2010, and he signed an entry-level contract with the Bruins on March 24, 2011.

Warsofsky spent most of the next four seasons with Providence of the American Hockey League, but made his NHL debut against the Buffalo Sabres on Dec. 19, 2013. He scored his first NHL goal in his fourth game, against the Ottawa Senators on Dec. 28.

He signed a one-year contract with the Pittsburgh Penguins on July 1, 2015, and was claimed on waivers by the New Jersey Devils on Feb. 29, 2016. Warsofsky returned to the Penguins on a one-year contract July 1, 2016, then signed a two-year contract with the Avalanche on July 1, 2017. He played 16 games, finished with five assists and averaged an NHL career-best 13:24 of ice time.