Labor's Louise Pratt has conceded defeat in the Western Australian Senate election rerun, and attacked the party process that delivered victory to her running mate Joe Bullock.

"It is a blow to progressive voters that I would be replaced in the Senate by someone who I have known for many years to be deeply homophobic, to be anti-choice and has recently emerged as disloyal to the very party he has been elected to represent," Pratt told reporters in Perth on Wednesday.

She denied it was a case of sour grapes.



Bullock, the right-leaning shop assistants' union stalwart, was backed by the powerful United Voice, which wanted to get left candidate Simone McGurk installed in the state seat of Fremantle.



This shunted Pratt to second place on the party's WA Senate ticket.



United Voice last week withdrew its support for Bullock after comments he made about Pratt at a Christian group function in November were revealed.



He had said Pratt was a "poster child" for same-sex marriage, some Labor members were "mad" and that he saw himself as a bulwark against "every weird leftie trend".



Pratt said she raised her concerns about Bullock with the national secretary and the national executive. So had others, but "these warnings were not heeded".



Factionalism had run roughshod over the party, the preselection process "and on occasion on policy", she said.

"I have pointed this out on many occasions that Labor was at risk of losing a second Senate seat here in Western Australia and I am ashamed that a factional power grab was privileged over principles deeply held by an overwhelming number of party members and indeed West Australians more broadly.



"It goes to the heart of the need for reform."



She labelled WA Labor "the least democratic" branch, saying the exertion of power by too few was eroding public trust in the party and in unions.



"If anything good comes from this devastating loss, it will be impetus for reform of our great party," Pratt said.



"The welfare of our nation depends on us getting our house in order."



Pratt denied unions members had too much say in Labor, instead blaming union powerbrokers, who ignored the views and needs of the working people they represented.



Pratt said WA's pre-selection of candidates was conducted with the lowest participation of rank-and-file members in the country.



She said she looked forward to hearing the strength of the remarks of opposition leader Bill Shorten after her defeat.



She ruled out seeking further roles within the Labor party, saying she would remain an ordinary branch member and did not have her sights on the state secretary position.



Pratt's defeat delivers a third seat to the Liberals, with the remaining two seats likely to go to Greens senator Scott Ludlam and Palmer United Party's Dio Wang. The final vote count will not be known until after Anzac Day.



Bullock is being sought for comment.