Opposition leader Mark McGowan made the announcement in Dianella last week, a suburb split between the two electorates.
Labor candidate Simon Millman will take 18 months off from his job as a lawyer at Slater and Gordon to campaign full-time.
Liberal member Michael Sutherland has held the traditionally Liberal seat since 2008 and it has not been confirmed if he will run in the next election.
“Mt Lawley will be a difficult seat. My opposition (if he runs) has the advantage of incumbency,” Mr Millman said.
Previously involved with the Beaufort Street Network, he lives with his wife and two young sons.
The electorate includes the suburbs of Mt Lawley, Yokine, Menora and Coolbinia, as well as sections of Dianella and Inglewood.
Current East Metropolitan Region MLC Amber-Jade Sanderson will attempt to make it into the lower house at the next election.
“I’ve represented the electorate of Morley as part of the East Metropolitan Region,” she said.
Ms Sanderson, who is a mother, lives in the electorate and attended John Forrest Secondary College.
The seat was historically held by Labor but Liberal Ian Britza won the seat at the last two elections.