LaCombe signed an eight-year contract with the Anaheim Ducks on Oct. 2, 2025. He said it was "an exciting day for my family and I am grateful to the organization for their belief in me. It was an easy decision for me to commit my future to the Ducks and Orange County."

About 2 1/2 months later, Lacombe was named to Team USA's roster for the Olympic Winter Games Milano Cortina 2026 as an injury replacement to Florida Panthers defenseman Seth Jones. At age 25, Lacombe became the third-youngest defenseman selected to the United States and fifth-youngest player for the 2026 Olympics. He helped the United States win gold at the 2025 IIHF World Championship for the first time in 92 years with five points (two goals, three assists) and a plus-11 rating. It was LaCombe's second gold medal in international competition following the 2021 IIHF World Junior Championship.

Anaheim's second-round pick (No. 39) in the 2019 NHL Draft had 43 points (14 goals, 29 assists) in 75 games of his second full NHL season. He was tied for seventh among NHL defensemen in even-strength goals (12) and 11th in goals, and third in goals among skaters 24 and under at his position behind Rasmus Dahlin (17) and Thomas Harley (16). His 14 goals were also the most by a Ducks defenseman since 2010-11 (Lubomir Visnovsky, 18) and he was one of eight defensemen in team history with at least 40 points, joining Scott Niedermayer (four times), Cam Fowler and Chris Pronger (three times), Oleg Tverdovsky (twice), and Dmitri Mironov, Fredrik Olausson and Visnovsky (once).

LaCombe had 99 points (19 goals, 80 assists) and was plus-53 in 140 NCAA games at the University of Minnesota from 2019-23, leading defensemen in points and goals in each of his final three seasons. He helped the Golden Gophers to the 2023 NCAA championship game as a senior and the Frozen Four three times (2020, 2022, 2023).