[2] In Fall 2010, having attended the Rangers' training camp and playing for the team during the pre-season, Stepan made the transition from Wisconsin to the NHL.

He scored a hat trick in his first NHL game on October 9, 2010, against Ryan Miller of the Buffalo Sabres, becoming the first rookie in Rangers history to do so, en route to a 6–3 victory.

[8] On the morning of July 27, 2015, just hours before his arbitration hearing was scheduled to occur, Stepan and the Rangers agreed to a six-year, $39 million contract lasting to the end of the 2020–21 season.

On June 23, 2017, Stepan (along with goaltender Antti Raanta) was traded to the Arizona Coyotes in exchange for the seventh overall pick in the 2017 NHL Entry Draft and defenseman Tony DeAngelo.

[12] On December 26, 2020, after three seasons with the Coyotes, Stepan was traded to the Ottawa Senators for a second-round pick in the 2021 NHL Entry Draft which originally belonged to the Columbus Blue Jackets.

[14] Before a trade could be completed, after registering 1 goal and 6 points through 20 games, Stepan suffered a dislocated shoulder injured in a 5-4 shootout victory over the Montreal Canadiens on February 23, 2021.

On March 2, 2021, it was announced that Stepan would undergo season-ending shoulder surgery to repair a damaged labrum, effectively ending his tenure with the Senators.

[16] Assuming a depth role among the Hurricanes forward group, Stepan tallied 9 goals and 19 points through 58 games in the 2021–22 season.

Un-signed through the following summer, Stepan continued with the Hurricanes in initially accepting a professional tryout contract to participate in training camp and pre-season for the following 2022–23 season.