New Greens leader, Richard Di Natale, has made an immediate appeal to the electoral mainstream, saying his party was “the natural home of progressive mainstream voters” and he was a non-ideological bloke who entered politics simply to “get stuff done”.

Di Natale was elected unanimously in a snap ballot after the shock resignation of Christine Milne. But Greens sources suggested Di Natale, and his fellow senators Scott Ludlam and Larissa Waters, who were elected co-deputy leaders, might have had prior knowledge of the ballot in a bid to sideline other potential candidates, including former deputy leader Adam Bandt.

Neither Di Natale nor Milne would answer repeated questions about whether she had given any senators warning of her resignation. Di Natale finally snapped that “someone may have been disappointed with the outcome. Surprise, surprise, that’s politics.” They said the process followed in the ballot was exactly the same as when Bob Brown stood down. And once Di Natale, like Bandt a Victorian, was elected leader, it was likely the deputy would have to be from a different state and probably also a woman.

Bandt tweeted his congratulations after the ballot, saying he was happy to stand down given his family was expecting a new baby shortly.

Adam Bandt (@AdamBandt) Congrats Richard & new team! V happy to hand over Deputy to focus on new baby (due in few wks!) & winning further Reps seats in Vic & NSW.

Di Natale, a former doctor from a working class Italian family who he said were traditional Labor voters, said no one got involved with the Greens unless “protecting the environment was in their DNA” and nominated getting the climate change debate “back on track” as a core goal. But he put a lot of emphasis on the party’s other policies, and explicitly voiced the intention to challenge Labor as the party opposing the Coalition’s cuts to health and education.

He said the Abbott government was “taking a hatchet to the social contract, to decent income support, to the health system, to education … and my job … is to ensure we are the opposition to Tony Abbott when it comes to those things”.

“I am not an ideologue … I just want decent government that looks after people. There are choices we have to make … My view is pretty straightforward. People want access to healthcare and education, and they want the environment looked after, and as a society we can afford to pay for those things.

“We just have some choices to make. You just have to decide whether we want to continue to give big handouts to mining companies through subsidies. You have to decide … whether you want to allow the super system to be used to minimise tax, you have to decide whether you want the multinationals to keep avoiding tax…”

Facebook Twitter Pinterest Former Australian Greens leader Bob Brown congratulates Christin Milne after her speech at the National Press Club in Canberra, in February 2013. Photograph: Alan Porritt/AAP

Milne said she had run a “cabinet style of leadership” which had allowed her colleagues to develop their skills, and she now believed they were “ready to fly”. All her parliamentary colleagues, as well as her predecessor Bob Brown paid tribute to her three years as leader.

After she resigned on Wednesday morning at what had been billed as a budget planning meeting, the 10 Green senators and one MP returned to their offices for a frantic hour of speed lobbying, before returning to conduct the ballot.

Di Natale, a former GP with a much lower national profile than either Milne or Brown, becomes leader as the party struggles to maintain its profile. The 2013 election result allowed the Abbott government to negotiate with a diverse crossbench in the Senate rather than Labor or the Greens, and the party faces imminent decisions on how far to cooperate with the Coalition on its second budget.

Milne first came to national attention in 1989 when, as a schoolteacher and mother of two young sons, she waged a successful campaign against the Canadian company Noranda’s proposal to build a pulp mill at Wesley Vale in Tasmania’s farming north-west where she lived. She was elected to the Tasmanian parliament that year, to the federal Senate in 2004, and became Greens leader in April 2012 when Brown stood down.

Facebook Twitter Pinterest Christine Milne says her successor Richard Di Natale has the potential to be ‘a wonderful asset.’

Under her leadership the Greens negotiated the carbon price agreement with the former prime minister Julia Gillard and sought to win more support in rural areas. But it has also been at times divided on strategy, including last year over how to handle the government’s proposed reintroduction of fuel excise indexation, with some arguing it should be supported because it would help reduce fossil fuel use. Milne and others prevailed with the view that the move should be opposed because the money was earmarked for spending on roads.

Di Natale said he had backed Milne in that decision, but would be discussing all aspects of the party’s budget response with his colleagues.

There was a nationwide swing of 3.34% against the Greens in 2013, as voters returned to the major parties after the tumultuous years of minority government, but the party increased its Senate representation by one to 10 senators, and Bandt retained the inner city seat of Melbourne.

Abbott said that despite their “very different political positions” he respected Milne’s commitment and public service. The Labor leader, Bill Shorten, congratulated her “on two and a half decades of distinguished public life”.

But the shadow treasurer, Chris Bowen, criticised the Greens’ closed door leadership selection process, saying it was “about as secret as the process to elect the Pope”. He suggested the Greens should follow Labor’s “confident and mature” process of allowing party members to have a vote on the party leadership. Greens senator Lee Rhiannon tweeted her support for a change of her party’s procedure yesterday.