Niemela was drafted 64th overall by the Leafs in the 2020 entry draft. The 21-year-old has since had a breakout year during the 2021-2022 season in the Finnish Elite League, before signing a three-year entry-level contract with the Leafs in May 2022. He led all defensemen in points during the 2021 IIHF World Junior Hockey Championship and played a crucial role for Team Finland in getting them to the gold medal game against Team Canada in 2022. Niemela took that almost game-winning shot on the wide-open Canada net that was famously blocked by
Mason McTavish, preventing Finland from stealing one from Canada.