A full bench of the High Court has ruled former Family First senator Bob Day was not validly elected as a senator and ordered a special recount of votes to determine his successor.
The Court found Mr Day profited from a lease arrangement at his South Australian electorate office, in violation of Section 44 of the Constitution.
Mr Day was not eligible to serve as an Australian senator from February 26 last year, the judges found.
A single judge will decide how the special recount for the South Australian Senate vacancy is conducted.
If first-preference votes for Mr Day are instead directed to Family First's second candidate on the ballot, lawyer Lucy Gichuhi, she will likely be elected.
SBS spoke with Lucy Gichuhi, Bob Day's likely replacement, about her political plans:
However, if Family First votes are instead distributed to other parties on the ballot, former Labor senator Anne McEwen could be the beneficiary.
The Australian Senate's official Twitter page confirmed there would be a further hearing before a single justice to figure out the details of the recount at an as-yet unknown time.
Section 44 of the Consitution holds that anyone with an "indirect pecuniary interest" in an agreement with the Commonwealth cannot be chosen as a senator.
The Commonwealth was making rental payments for Bob Day's electorate office in South Australia to a company called Fullarton Investments.
That company had financial ties to Bob Day's family trust, and directed the Commonwealth to pay rent into a bank account owned by Mr Day. On this basis, the court decided the former senator was in breach of Section 44 when he was elected.
The court also ordered the Commonwealth to pay Mr Day's legal costs.
Labor released a press statement condemning the Turnbull government for failing to act on allegations against Bob Day earlier.
Labor's Mark Dreyfus referred to comments made by finance minister Mathias Cormann in November last year, when he said a day in late December 2015 was "the first time I became aware of the arrangements put in place in relation to then Senator Day's electorate office".
"It was not until August 2016 that the government could no longer ignore the mounting pressure, and was finally forced to take action against Bob Day," Mr Dreyfus' press release reads.
"Malcolm Turnbull turned a blind eye to doubts about Bob Day’s eligibility to be a Senator because he wanted Mr Day’s vote to get his regressive legislation through the Senate."
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