The 19-year-old forward, selected with the No. 18 pick of the 2020 NHL Draft, is the first of three Devils first-round picks to agree to a contract. Forward
Alexander Holtz
, the No. 7 choice, is playing for Djurgarden in the Swedish Hockey League, and defenseman
Shakir Mukhamadullin
, the No. 20 selection, is playing with Ufa in the Kontinental Hockey League.
"It's really exciting," Mercer said. "It's another step toward my goal. And to finally happen here at Christmas, it's a pretty nice gift for me and my family. The draft was one thing and then getting signed was another, and now the next step is finally getting there and getting started with the organization."
Mercer scored seven points (four goals, three assists) in five games with Chicoutimi of the Quebec Major Junior Hockey League this season before leaving to play for Canada at the 2021 IIHF World Junior Championship, which starts Friday. Last season he scored 60 points (24 goals, 36 assists) in 42 QMJHL games with Drummondville and Chicoutimi, and helped Canada win the 2020 WJC.
Holtz (Sweden) and Mukhamadullin (Russia) also are playing at the 2021 World Junior Championship.
The Devils were 14th in the Eastern Conference with a .493 points percentage (28-29-12) last season, but their roster includes forwards Nico Hischier, the No. 1 pick of the 2017 NHL Draft, and Jack Hughes, the No. 1 pick of the 2019 NHL Draft.
As one of the seven teams to not take part in the NHL Return to Play Plan last season, they can open training camp Dec. 31. Their first game is against the Boston Bruins at Prudential Center on Jan. 14.
"I'm really happy to be drafted by the Devils," Mercer said. "Seeing the young prospect pool that we have, just sizing up for the future, I'm really excited. I think there's a lot of damage that we can do with the group that we have, and I think getting in right now is the right time and a great situation for me to hopefully transition to the NHL."
NHL.com staff writer Mike G. Morreale contributed to this report
