Western Australian party faithful gathered at the Whale and Ale pub on the northern outskirts of Perth on Monday night where Ms Aitken edged out former navy officer Miquela Riley.
Ms Aitken will take on her council colleague and Labor's pick of City of Wanneroo mayor Tracey Roberts at next year's election. But her nomination will first need to be rubber stamped by the party's state executive when it comes before them on Thursday.
The plebiscite was the first time the Liberals let rank and file members vote for their preferred candidate in a Liberal-held seat.
WA Liberal party state president Richard Wilson said Ms Aitkin was the best person to represent Pearce.
"Linda will work hard in the months ahead to meet with as many locals as possible, to listen to the issues that are important to them and their family, and share her positive ideas for Pearce", Mr Wilson said.
"As a strong local voice, Linda has been helping to deliver better services for her community. She understands the issues which are important to the people of Pearce because her family experiences them every day."
Mr Porter announced he wouldn't recontest his seat at the next election after a scandal-ridden 2021 when he was demoted within the federal cabinet before being forced to resign altogether.
The former attorney-general held Pearce since 2013 and it's been in Liberal hands since its inception in 1990.
Mr Porter retained it at the 2019 election on a 7.5 per cent margin but it's now considered a much tighter contest after a boundary redistribution.
The election is due to be held by May.
Mr Porter sued the ABC after it published a story about allegations an unnamed cabinet minister had raped a now-deceased woman in 1988.
He strenuously denied the allegations after outing himself as the accused minister and has since settled a defamation case against the national broadcaster.
But it was then revealed in September anonymous donors had paid for part of Mr Porter's legal fees.
Mr Porter denied any conflict of interest and said no banned donors contributed money to the fund, but nonetheless tendered his resignation from cabinet rather than publicly reveal the donors.
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