On 7 November 2016 under section 376 of the Commonwealth Electoral Act 1918, the Senate referred two matters to the High Court. Both involved the qualification of senators under section 44 of the Constitution. The first involved a possible pecuniary interest relating to the lease for an electoral office for former Senator Day, who had resigned as a senator for South Australia on 1 November. The second matter related to Senator Culleton and involved a conviction for larceny which was subsequently annulled, but had stood throughout the election period.
On 18 December 2016, Senator Culleton resigned from Pauline Hanson's One Nation Party to sit as an independent senator. On 11 January 2017, the President of the Senate informed the Governor of Western Australia of a vacancy due to Senator Culleton being disqualified from the position due to a declaration of bankruptcy.
On 3 February 2017 the Court of Disputed Returns determined that Mr Culleton had not been validly elected in the 2016 election, and that the vacancy in the representation of Western Australia should be filled by a recount of ballots. The recount occurred on 7 March 2017, and as a result Peter Georgiou from Pauline Hanson's One Nation Party was elected to fill the vacancy.
In a judgment handed down on 5 April 2017, the Court of Disputed Returns found that Mr Bob Day had not been validly elected and ordered a special count of ballots to fill the vacancy. The recount was conducted on 13 April and, on 19 April 2017, the High Court declared Lucy Gichuhi as a senator for South Australia. Senator Gichuhi has indicated that she will sit as an independent senator.
On 7 February 2017, Senator Bernardi announced his resignation from the Liberal Party and now sits as an Australian Conservatives senator.