He represented the electoral district of Saanich North and the Islands as a member of the Green Party of British Columbia caucus until 2024.

[1] Olsen previously ran in the same district in the 2013 provincial election, losing narrowly to Gary Holman.

On May 29, NDP leader John Horgan and Green leader Andrew Weaver announced that the Greens would provide confidence and supply to an NDP minority government, a position which was endorsed the following day by the members of both caucuses.

[6] On December 20, 2019, Olsen was appointed interim leader, following the resignation of Andrew Weaver.

[7] Olsen is a member of the Tsartlip First Nation in Brentwood Bay and served as a two-term Central Saanich Councillor prior to his election.