On 3 May 2017, Westerholm left Brynäs alongside brother Pathrik, and signed a two-year contract with Frölunda HC.[2]
After claiming the Swedish Championship in his final season under contract in 2018–19 season, Westerholm left as a free agent to move to the Finnish Liiga, again alongside Pathrik, agreeing to a one-year deal with Lukko on May 8, 2019.[3]