Prime Minister Anthony Albanese and Birmingham’s Senate sparring partner,government Senate leader Penny Wong,lauded the South Australian for being an articulate and earnest politician as he implored Liberals to trumpet free-market and pro-immigration policies.

Birmingham argued Australian attitudes hewed towards the middle ground rather than the fringes and that major parties forgot this “at their peril”.

He explained that he did not always agree with Dutton but believed the Coalition leader understood the need to win over mainstream voters as someone who was “thoroughly decent[with] a perspective in touch with many hard-working Australians”.

“It is not necessary to target one another and personalise debates to advance the issues important to you. It is not necessary to undermine the principles and practices at this Senate to advance the issues important to you,” Birmingham said.

The opposition leader hugged Birmingham after the speech as politicians across the spectrum applauded the senator’s career.

Birmingham’s departure will diminish the power of the more centrist moderate grouping within the Coalition,whose numbersdwindled when six inner-city Liberals lost their seats to teals in 2022. Jane Hume,Paul Fletcher and Andrew Bragg are top moderate figures.

Birmingham was criticised privately by some moderate allies over the years for failing to argue more forcefully against conservatives in shadow cabinet. Some of his right-wing colleagues felt Birmingham lacked the political firepower to tackle Labor.

Wong said he had often displayed kindness and an ability to rise above the fray.

“He is a thoroughly decent person,” Wong said.

Cash will become the opposition leader in the Senate. Anne Ruston will become the deputy,moving up from the manager of opposition business. Frontbencher Jonathon Duniam will lead opposition business.

Dutton said Birmingham would have become one of Australia’s best foreign ministers. His resignation will set off an intense preselection contest in the faction-riven South Australian Liberal divisiondominated by right-wing forces attached to Senator Alex Antic.

“He has stood steadfastly with Israel and been a voice of moral courage and clarity at a time when our ally has been treated by some as an adversary. And he has nurtured and cultivated relationships which are central to the endeavours of AUKUS,” Dutton said in a statement.

Birmingham came into parliament in 2007,replacing former senator Jeannie Ferris on a casual vacancy in May and was elected in his own right that year.

He entered the ranks of the shadow outer ministry,promoted by then-opposition leader Malcolm Turnbull two years later. Birmingham entered the cabinet under Turnbull during his prime ministership and successfully landed a landmark funding deal while education minister. He later held the trade and tourism portfolios and then the finance ministry.

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