Independent Kerryn Phelps was repeatedly referred to as a “high-profile” candidate during the Wentworth by-election, a candidate considered a dark horse, but who captured voters’ imaginations with personality and an impressive resumé.

Dr Phelps, a GP and Sydney City councillor running against the Liberal Party’s Dave Sharma and Labor’s Tim Murray, quickly emerged as the firm favourite in the Liberal stronghold, and came through on Saturday to deliver the Liberals’ biggest defeat in their history.

The Liberal Party had never lost the Wentworth seat, vacated by former prime minister Malcolm Turnbull following the spectacular leadership spill in August.

Dr Phelps’ crushing victory was clearly a barometer of voters’ dissatisfaction with political instability, a protest vote the likes of which Australia has never seen.

The swing was the largest against a government in a by-election in the history of Australian politics.

The loss resulted in the Morrison government losing its slim majority in Canberra, meaning it will be forced to govern as best it can with the help of cross-benchers in the lower house.

Dr Phelps told supporters the victory was one “for the people of Wentworth …  but more broadly than this, this victory is for the people in Australia who need a voice”.

She thanked her wife, Jackie, and the supporters of her campaign, portraying it as a “David and Goliath struggle”.

“We have been up against the major parties with all of their infrastructure and all of their resources and here we were, a little pop-up campaign with three weeks’ notice to put [it] together,” she said on Saturday.

Before the by-election, she said “the people of Wentworth are crying out for an authentic voice who will stand up to the major parties and rise above the bitterness and backstabbing that has taken over Canberra”.

However, she later told reporters she would not be a “destabilising influence if elected”, vowing to not block supply for the government.

Kerryn Phelps in her robes as the Australian Medical Association president. Photo: AAP

The former head of the Australian Medical Association (AMA) presents a mix of seemingly opposing political views, putting fiscal conservatism alongside progressive positions on climate change, asylum seekers and social inclusion.

Before running as an independent candidate, Dr Phelps was also a strident gay-marriage campaigner as a member of LGBTQI community.

The 60-year-old, from the Pittwater region of Sydney, married Jackie Stricker-Phelps in a religious ceremony in New York in 1998.

The couple has a young daughter, Gabrielle, while Dr Phelps has two children from her first marriage to Michael Fronzek.

The independent candidate’s decision to preference the Liberals’ Mr Sharma, ahead of Labor’s Tim Murray was criticised by some voters who saw her environmental policy more aligned with Labor.

The Liberal Party tried to attack her for perceived political flakiness – a sign of her “path to power” – highlighting Fairfax Media reports that she had enrolled as a Liberal member in 1994 to contest pre-selection for the federal seat of North Sydney, and had also been in discussions with Labor officials about joining Mark Latham in 2004.

Dr Phelps has denied the claims, saying she is an independent and has never stood for pre-selection for a major party.

The independent candidate also received support from Greens leaders Richard Di Natale and former leader, Bob Brown.

In a controversial intervention to help Dr Phelps win the seat, Mr Brown urged Greens voters to ignore the party’s how-to-vote cards in Wentworth.

Dr Kerryn Phelps (right) and her partner by marriage Jackie Stricker in 2005. Photo: AAP

Brown told the Financial Review he feared that following Greens preferences could push Labor candidate Mr Murray into second spot, relegating Dr Phelps to third position and causing most of her preferences to go to Mr Sharma.

In addition to her work with the AMA, Dr Phelps is among a movement of preventative health practitioners, authoring books on “wellness”, recent research in gut health as well as complementary lifestyle therapy for cancer treatment and sex education.

She co-authored The Mystery Gut, a guide into common gut conditions and improving gut health; The Cancer Recovery Guide and Sex: Confronting sexuality.