Sennecke was named a finalist for the 2026 Calder Trophy given to the NHL rookie of the year. His 23 goals tied New York Islanders defenseman Matthew Schaefer for most among first-year players and he was second in assists (37) and points (60) to help the Anaheim Ducks clinch their first Stanley Cup Playoff berth since 2017-28. He also had 13 power-play points, took the most shots on goal among forwards (197) and averaged 17:27 of ice time per game. Sennecke additionally became the third rookie in Ducks history to play all 82 games of a season, joining Cutter Gauthier (2024-25) and Dustin Penner (2006-07).

His 18 goals as a teenager were the most in a single season and by one in Ducks history. His 23 goals were tied for third all-time among Ducks rookies, trailing only Bobby Ryan (31) and Penner (29). He was also the youngest Ducks player to reach 60 points and the only one to do so within the first two seasons following his draft.

Sennecke joined a blossoming Ducks core after he was selected No. 3 at the 2024 NHL Draft. He signed an entry-level contract July 5, 2024. He had 68 points (27 goals, 41 assists), scored seven power-play goals and led Oshawa of the Ontario Hockey League with seven game-winning goals in 63 regular-season games. His 10 goals in 16 games were tied for fourth in the OHL playoffs. In 2022-23, Sennecke was named to the OHL Second All-Rookie Team after he had 55 points (20 goals, 35 assists) in 61 games.

The Toronto native represented Team Canada White at the 2022 World Under-17 Hockey Challenge, where he had three assists in five games.