1 The Country Party (CP) contested the elections in Western Australia as the National Alliance (NA), which was a merger of the CP and the Democratic Labor Party (DLP) in that state. The NA won a single Senate seat in WA, its elected representative being Tom Drake-Brockman, who represented the CP, on election to parliament. 2 Independent: Michael Townley (Liberal Party from Feb 1975)
Gough Whitlam had been an active prime minister since his party's victory in the 1972 election, and his government had pursued many socially progressive reforms and policies over its first term. However, it received a hostile reception from the coalition/DLP-controlled Senate, with the last Senate election held in 1970.
On 21 March, Whitlam announced there would be a half-Senate election on 18 May.
Following an attempt by Whitlam to create an extra Senate vacancy in Queensland by appointing former Democratic Labor Party (DLP) Leader, Senator Vince Gair, as Ambassador to the Republic of Ireland, Snedden announced that the opposition would block the Government's supply bills in the Senate. After a great deal of legalistic argumentation in both houses about the Gair matter, and justified by the failure of six (non-supply) bills to pass the Senate, Whitlam requested and was granted by Governor-General Sir Paul Hasluck a double dissolution under section 57 of the Constitution. The already-announced election date of 18 May was kept. The election focused on Whitlam's first one-and-a-half years in office and whether the Australian public was willing to continue with his reform agenda.
The re-elected Whitlam government's failure again to gain a majority in the Senate led to Australia's only joint sitting pursuant to section 57 of the Constitution. It was approved by the new governor-general Sir John Kerr after the bills were presented to the new parliament and were rejected a third time. It was held three months after the election, on 6–7 August, and it enabled the six bills that had been thrice rejected by the Senate to be passed. The Health Insurance bills were both passed on party lines, 95–92, the Petroleum and Minerals Authority legislation also passed on party lines, though with one Liberal Party member absent. Liberal Movement Senator Steele Hall supported the three Electoral bills, citing his experience as Liberal Premier of South Australia, where he had fought his own party in an effort to improve unequal electoral arrangements dubbed the Playmander. Northern Territory Country Party MP Sam Calder supported the Territory Senators legislation, though he opposed the ACT being given added representation.
The Whitlam Government had been re-elected with their majority in the House of Representatives reduced from 9 to 5 seats, while they gained 5 seats in the Senate. The ALP and the coalition each won 29 seats in the 60 member Senate, with the balance of power held by Steele Hall of the Liberal Movement, and Michael Townley, a conservative independent. Despite the lowered quota, the Democratic Labor Party lost all five of its Senate seats. When the joint siting was held between the two chambers, the ALP held 95 of the 187 seats, giving them a narrow 3-seat majority.
In February 1975, Townley joined the Liberal party.
Later in 1975, Coalition premiers would break longstanding convention in the replacement of two ALP senators. Lionel Murphy, who had resigned to take up an appointment to the High Court, was replaced by independent Cleaver Bunton; and Bertie Milliner, who had died, was replaced by Albert Field, an ALP member who was opposed to Whitlam. Bunton (along with Hall) refused to vote against supply, but Field was prepared to. Field took his seat in the Senate as an Independent on 9 September. Due to a High Court challenge to his appointment, he was on leave from the Senate, unable to exercise a vote, from 1 October 1975, which reduced the number of sitting senators to 59. This gave the Coalition an effective majority, holding 30 of the 59, allowing them to block supply in the Senate to pave the way for the 1975 Australian constitutional crisis.