In the Australian state of Western Australia, the Leader of the Opposition is the leader of the largest minority political party or coalition of parties in the Legislative Assembly of the Parliament of Western Australia.

By convention, the leader is generally a member of the Legislative Assembly.

The notion of leader of the opposition was well understood, however, and on occasions was applied to members.

Maitland Brown, for example, was often referred to as "Leader of the Opposition" during his period as an outspoken critic of Governor Robinson's Government.

At the March 2021 election, the National Party, previously in the crossbench, won more seats than the previous opposition Liberal Party in the Legislative Assembly.