Mayo voters have roundly endorsed Rebekha Sharkie, returning the Centre Alliance candidate to federal parliament with a strong swing in Saturday’s by-election.

Liberal candidate Georgina Downer conceded defeat two hours after the close of the polls, with Ms Sharkie to head back to Canberra after being forced to resign over the dual citizenship saga.

She was expected to finish with about 55 per cent of the two-party-preferred vote, increasing her margin by more than three percentage points after a 10 per cent swing on the primary vote.

“I was crushed the day I resigned but today was sweet,” she told supporters in Mt Barker.

“Tonight we have shown that you don’t need lots of money, that you don’t need a big political machine.

“What you need are people who are passionate, people who care.”

Liberal candidate Georgina Downer concedes after her defeat by Centre Alliance’s Rebekha Sharkie. Photo: AAP

Ms Downer said Ms Sharkie put up an extremely good fight to retain the seat.

“Ultimately this was a by-election about the people of Mayo and I absolutely respect their decision,” she said.

“We always knew it would be a particularly challenging campaign.”

Earlier Liberal frontbencher and SA MP Christopher Pyne described Mayo as a “pretty straightforward result”.

“Being an independent (Ms Sharkie) never actually has to disagree with anybody. She can be on everyone’s side on every argument and that always makes it tricky to dislodge an independent,” he told Sky News.

Ms Downer has vowed to stand again at the next federal election in 2019, but will be faced with an even tougher task to return Mayo to the coalition benches.

Despite her family connections to the area – her father Alexander held the seat for 24 years from 1984 – Ms Downer had to counter suggestions she was something of a blow-in after living interstate or overseas for much of the past 20 years.

Ms Sharkie campaigned hard on her background as a long-standing member of the local community, that homespun image appearing to work in her favour.

She was criticised for too often supporting Labor in the parliament, something she, and apparently, the voters, rejected.