However, due to several players being out with injuries in Bern, Hischier was brought to the top team on 13 November that year, playing with his brother.

[3] Hischier's first season with the Mooseheads saw him finish second to Maxime Fortier for the team scoring lead, and tenth overall in the QMJHL, with 38 goals and 86 points.

For this Hischier was awarded the RDS Cup for being the QMJHL Rookie of the Year and the Michael Bossy Trophy as the best professional prospect in the league.

[7][8] Ranked the second-best North American skater in the NHL Central Scouting Bureau final list prior to the draft, Hischier was highly regarded as a tremendous offensive talent with exceptional hockey sense.

[14] After a strong training camp and preseason, where he led the Devils in scoring with seven points in four games, Hischier made the opening-day roster.

[16] He recorded his first point, an assist, on 9 October in his second game, against the Buffalo Sabres, while his first two goals came ten days later against Craig Anderson of the Ottawa Senators.

[17] Hischier finished the regular season as the Devils' second best scorer (behind Hart Trophy-winning linemate Taylor Hall) with 52 points, including 20 goals and 32 assists.

After the Devils were eliminated from the 2018 Stanley Cup playoffs in five games by the top-seeded Tampa Bay Lightning, Hischier revealed he had been playing with a hand injury that kept him out of the 2018 IIHF World Championship.

Although the injury initially only projected him to miss three weeks of NHL action,[28] the surgery for Hischier's broken nose ended up sidelining him a total of 24 games.

"[30] On 27 October 2023, Hischier suffered an upper-body injury resulting from a check to the head by Buffalo Sabres defenceman Connor Clifton.

[2] He also participated in the 2017 World Juniors, scoring four goals and had seven total points in five games, the most by any player eligible for the 2017 NHL entry draft.

[41] After being selected by the Devils, general manager Ray Shero cited both Hischier's speed and commitment to defence as reasons for picking him first overall, seeing it as ideal for the team.

[42] Head coach John Hynes, speaking after the draft, commended Hischier on "how he competes on the puck and his speed, skill set and hockey sense," saying they were already "at an NHL level.

"[43] Hischier comes from a family of athletes; his father Rino played football for FC Naters and his mother Katja worked as a sports teacher.