Moritz Seider made the Opening Night roster for the Detroit Red Wings to start the 2021-22 season after playing all but one of the prior four seasons in his native Germany and Sweden. He was named the NHL Rookie of the Month for October, the first Red Wings player to earn the honor since Dylan Larkin in November 2015, building on the success he enjoyed playing with and against professionals. He became the 10th defenseman in the past 40 years to score at least 50 points as a rookie and one of three active players at the position to (Quinn Hughes and Cale Makar in 2019-20).

He made his pro debut for Grand Rapids in the American Hockey League shortly after Detroit selected him with the No. 6 pick in the 2019 NHL Draft, and played 2021 for Rogle BK of the Swedish Hockey League. Seider scored 28 points (seven goals, 21 assists) in 41 regular-season games and five points (one goal, four assists) in 13 playoff games, winning the SHL Elite Prospect's Award and being named a finalist for SHL Defenseman of the Year.

Seider was captain for Germany at the 2020 IIHF World Junior Championship and named a top three player after getting six assists in seven games.

Seider won the Calder Trophy as NHL rookie of the year in 2021-22. He led rookie defensemen with 43 assists and 50 points. He was the first Red Wings rookie defenseman with at least 50 points in a season since Nicklas Lidstrom (60) in 1991-92. Seider also was the first Red Wings player to win the award since goalie Roger Crozier in 1964-65. His four assists tied Mike Green's Red Wings record by a defenseman set Oct. 5, 2017 in a 7-5 win against the Winnipeg Jets at Little Caesars Arena on Jan. 10, 2023. Three of Seider's assists came in the first period, making him the first Detroit skater since Anthony Mantha in the third Feb. 20, 2019 to get as many in one period.

Seider signed a seven-year, $59.85 million contract (average annual value of $8.55 million) with the Red Wings on Sept. 19, 2024, and became the second Detroit defenseman with at least 40 points in each of his first four seasons (Brian Rafalski, four from 2007-08 to 2010-11). He played for Team Germany at the Olympic Winter Games Milano Cortina 2026, where he led all skaters by averaging 26:16 of ice time per game.