Keller hasn't let a lack of size (5-foot-10, 170 pounds), keep him from making a big impact in the NHL. The native of Chesterfield, Missouri, is among the new generation of small, nimble forwards such as Patrick Kane of the Chicago Blackhawks and Johnny Gaudreau of the Calgary Flames who have the skill to beat bigger opponents without taking a pounding.
After breaking Phil Kessel's record for points by a player in the USA Hockey National Team Development Program from 2014-16 (189), Keller was selected by the Arizona Coyotes in the first round (No. 7) of the 2016 NHL Draft. He played one season at Boston University, finishing with 45 points (21 goals, 24 assists), and helped the United States finish first at the 2017 IIHF World Junior Championship before signing with the Coyotes on March 26, 2017. Three days later, Keller had an assist in his second NHL game against the St. Louis Blues.
Keller scored his first NHL goal to open the 2017-18 season against the Anaheim Ducks and continued to pile up goals and points despite the Coyotes' slow start. He scored 11 goals in Arizona's first 16 games and reached the end of 2017 leading the Coyotes in goals, assists and points, although he was still more than six months away from his 20th birthday.
He finished his first NHL season with 65 points (23 goals, 42 assists) and was a finalist for the Calder Trophy, given to the top rookie in the NHL.
Keller signed an eight-year contract extension Sept. 4, 2019 that is set to begin in the 2020-21 season.