The Chicago Blackhawks thought highly enough of Schmaltz to select him in the first round (No. 20) of the 2014 NHL Draft. And that was before he helped the University of North Dakota win the 2016 NCAA championship by defeating Quinnipiac. He also scored the winning goal against the University of Denver with 57 seconds left in the third period to put North Dakota in the championship game.

Schmaltz scored 11 goals and 46 points in 37 games as a sophomore as the center on North Dakota's top line in 2015-16 and his 35 assists were fifth in the NCAA and the most by a North Dakota player since future NHL forward T.J. Oshie had 35 in 2006-07. He was third nationally at plus-44 and first with 28 even-strength assists. His 0.95 assists-per-game ratio was fourth best in the NCAA.

As a freshman in 2014-15, Schmaltz played with his older brother Jordan, a first-round pick (No. 25) of the St. Louis Blues in the 2012 NHL Draft. Nick Schmaltz was named to the National Collegiate Hockey Conference All-Rookie Team after scoring 26 points in 38 games. He led North Dakota freshmen in scoring and was fourth on the team, right behind Jordan (28 points).

Schmaltz played a prominent role for the United States at the 2016 IIHF World Junior Championship, scoring two goals and eight points in seven games en route to a third-place finish. He led the U.S. with eight points (five goals) and won silver at the Ivan Hlinka Memorial Cup in 2013.

Before his college days, Schmaltz played for Green Bay of the United States Hockey League for two-plus seasons. At 17 he was the youngest player named to the USHL All-Rookie team in 2012-13 after scoring 18 goals and 52 points in 64 games.

Schmaltz signed a three-year, entry-level contract with Blackhawks on June 19, 2016. He was traded to the Arizona Coyotes on Nov. 25, 2018 but sustained a lower-body injury Dec. 30 that sidelined him for the remainder of the season. He signed a seven-year contract with the Coyotes on March 30, 2019.

Schmaltz had seven points (two goals, five assists) to set an Coyotes/Winnipeg Jets record for most in one game in an 8-5 win against the Ottawa Senators at Gila River Arena on March 5, 2022. He became the first player to score at least seven points in an NHL game since Sam Gagner scored eight (four goals, four assists) for the Edmonton Oilers against the Blackhawks on Feb. 2, 2012. He also was the first player to get seven points without a hat trick since Eric Lindros (one goal, six assists) for the Philadelphia Flyers against the Senators on Feb. 26, 1997.

Schmaltz became a member of the Utah Hockey Club effective June 13, 2024, after the NHL established a new franchise in Salt Lake City on April 18 of that year. He played a full, 82-game season for the first time and had an assist for his 400th NHL point in Utah's 3-2 overtime loss to the Pittsburgh Penguins at Delta Center on Jan. 29, 2025. Schmaltz signed an eight-year, $64 million contract with the Utah Mammoth on March 11, 2026. His 24 goals at the time of the signing set a new NHL career high and he led Utah with five multigoal games.