Known as a defensively-minded forward, Lehkonen famously scored series-winning overtime goals in two consecutive Stanley Cup semifinals against the Vegas Golden Knights (2021) and Edmonton Oilers (2022).

[1] On 28 March 2014, Lehkonen opted to leave KalPa of the Finnish Liiga and further his development in the Swedish Hockey League (SHL), in signing a two-year contract with Frölunda HC.

The Canadiens qualified to the 2021 Stanley Cup playoffs in the final wildcard spot, and embarked on an unexpectedly deep run, defeating the Toronto Maple Leafs and the Winnipeg Jets in the first two rounds.

[8] Following the team's loss to the Tampa Bay Lightning in the Finals, the Canadiens re-signed Lehkonen to a one-year, $2.3 million contract extension.

[9] Following the Finals appearance, the 2021–22 season saw the Canadiens perform historically poorly, resulting in the sacking of longtime general manager Marc Bergevin.

"[8] On 21 March 2022, Lehkonen was traded by the Canadiens to the Colorado Avalanche in exchange for Justin Barron and a second-round pick in the 2024 NHL entry draft.

[14] In Game 4 of the series, Lehkonen scored the series-clinching goal in overtime to win the Clarence S. Campbell Bowl and send his team to the Stanley Cup Finals for the second consecutive year.

[19] Ismo has worked for Yle as a hockey commentator, notably being present in Amalie Arena in 2022 to cover his son's victory in the Stanley Cup Finals.