Kelly McManus, a staffer for David Templeman MLA, has withdrawn from Labor's preselection contest for the upcoming Canning byelection.
Ms McManus, a long-time research officer for the Mandurah MP, withdrew on Wednesday ahead of a ballot of local party members on Sunday.
It is understood her withdrawal was to make way for the preselection of Law Society president Matt Keogh.
"For 20 years I have served the Labor Party," Ms McManus said.
"I look forward to doing so for the next 20 years.
"It was an honour to have been encouraged to nominate by friends and people I deeply respect.
"There have been lots of conversations over the last couple of days.
"I have come to the view that Matt will be a fantastic candidate for Canning and I am very keen to support his campaign.
"This weekend I will be out in the field urging people to vote for Matt Keogh and Labor."
Labor's candidate will be decided at a meeting this Sunday.