A first-round pick (No. 9) by the Winnipeg Jets in the 2014 NHL Draft, the Aalborg, Denmark, native made the roster for the 2015-16 season as a 19-year-old coming out of his first NHL training camp.

After a scoreless debut against the Boston Bruins on Oct. 8, 2015, Ehlers had a point in eight of his next nine games. The speedy left wing earned his first two assists on a pair of Mark Scheifele goals in Winnipeg's second and third games. A slap shot blasted past New York Rangers goalie Henrik Lundqvist in Winnipeg's 4-1 win on Oct. 13, 2015, gave Ehlers his first NHL goal.

After scoring goals in three consecutive games against the Tampa Bay Lightning, Minnesota Wild and Los Angeles Kings in October 2015, Ehlers earned his first multipoint game on Jan. 26, 2016, with three goals in a 5-2 home win against the Arizona Coyotes. That made Ehlers the first rookie to have a hat trick for the Jets/Atlanta Thrashers since Kamil Piros against the Lightning on April 6, 2003.

Despite ranking 11th among Winnipeg's skaters in total ice time, Ehlers finished tied for sixth in scoring with 38 points and fifth with 167 shots.

He broke out in 2016-17, finishing with 64 points (25 goals, 39 assists), and scored at least 21 goals in each of the next three seasons, including 29 in 2017-18. He signed a seven-year contract with the Jets on Oct. 3, 2017, and was the third player in Jets history since the franchise relocated to Winnipeg in 2011-12 to play his 500th NHL game Feb. 22, 2023,

Ehlers got his 474th point in Winnipeg's 7-4 win against the Lightning at Canada Life Centre on Nov. 3, 2024, to break Frans Nielsen’s record of 473 for most by a Denmark-born player in NHL history. He signed a six-year, $51 million contract with the Carolina Hurricanes on July 3, 2025, and was  one of the first six players named to Team Denmark for the Olympic Winter Games Milano Cortina 2026. His game-winning goal in a 4-2 win against Team Latvia on Feb. 16, gave Denmark its first victory in an Olympics involving NHL players. Ehlers also became the country's first skater with three points in an Olympics with NHL participation.

Ehlers' father, Heinz, was taken by the Rangers in the ninth round (No. 188) of the 1984 NHL Draft, gave a number of hints he could be a dynamic presence in the League. As a rookie with Halifax of the Quebec Major Junior Hockey League in 2013-14, Ehlers finished fourth in the league in scoring with 104 points and led all first-year players in goals (49), assists (55) and points.

Ehlers also led the QMJHL with a plus-65 rating, earned awards as the league's top rookie, top offensive rookie and top prospect, and selections to the QMJHL All-Rookie Team and its Second All-Star Team.