An election for all Senate seats was held on 2 July 2016 after the dissolution of the Senate on 9 May. The Senate now contains its largest cross-bench of 21 senators (7 AG and 14 others), compared with 18 senators (10 AG and 8 others) at the end of the 44th Parliament. Previously, the highest number had been 13 senators, in 2002-2005.
On 31 August 2016 state senators were divided into two classes: short-term senators whose terms expire on 30 June 2019, and long-term senators whose terms expire on 30 June 2022. These classes were allocated according to the order of election. Details of terms of service are available on this page.
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.
The Court of Disputed Returns found that neither senator had been validly elected and in each instance a recount of ballots was ordered. As a result Peter Georgiou from Pauline Hanson's One Nation Party was elected to replace Senator Culleton, and Lucy Gichuhi from Family First was elected to replace Senator Day. Senator Gichuhi later indicated that she would 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.
Senators Ludlam and Waters of the Australian Greens announced their resignations, on 14 and 18 July 2017 respectively, due to dual citizenship (see section 44(i) of the Constitution). It is expected that both matters will be referred to the Court of Disputed Returns when the Senate returns in August.
Senator Back resigned as a senator for Western Australia on 31 July 2017. The vacancy will be filled in accordance with section 15 of the Constitution.