Five electorates will head to the polls on Saturday for a series of federal by-elections that could change the composition of federal Parliament and provide a referendum on the leaderships of Prime Minister Malcolm Turnbull and Opposition Leader Bill Shorten.

With no opposition having lost a by-election to a sitting government in 98 years, there is much at stake for Labor, which faces the prospect of losing its seats in Tasmania’s Braddon and Queensland’s Longman.

Here’s a rundown of all five seats up for grabs on what has been billed as ‘Super Saturday’.

Longman, Queensland

Former Labor MP Susan Lamb will recontest the seat of Longman, north of Brisbane, after being forced to resign in May due to revelations she held dual British citizenship.

Ms Lamb, elected with a margin of just 0.8 per cent, will face a tough challenge from Liberal National Party candidate Trevor Ruthenberg.

Preferences from One Nation’s candidate Matthew Stephen will be critical in determining whether Mr Ruthenberg can defeat Ms Lamb.

Susan Lamb has her work cut out to regain the seat. Photo: AAP

With a field of 11 candidates, it is expected that minor parties and independents could poll well.

Braddon, Tasmania

Labor’s Justine Keay held the seat of Braddon, northwestern Tasmania, with a 2.2 per cent margin and is attempting to be re-elected after resigning in May over her dual British citizenship.

Ms Keay is behind in the polls and the betting markets, with Brett Whiteley – who held the seat from 2013 but lost in the 2016 election – on track for a narrow win.

The PM and Mr Shorten have campaigned heavily in the seat, which is being contested by eight candidates.

Mayo, South Australia

The Centre Alliance’s Rebekha Sharkie is gunning for the seat of Mayo, after resigning in May over her dual British citizenship.

Ms Sharkie won the seat, which takes in the Adelaide Hills through to Kangaroo Island, with a 5 per cent margin.

Ms Sharkie is expected to retain the seat, but faces a challenge from the Liberals’ Georgina Downer, the daughter of former federal minister Alexander Downer.

The tactic of bringing in the star candidate of Georgina Downer may backfire on the Liberals. Photo: AAP

If elected Ms Downer would become the fourth generation of her family to serve in federal Parliament, however she has been battling local perceptions of being out of touch and having been parachuted into the seat.

Perth, Western Australia

The West Australian seat of Perth became vacant after the resignation of Labor’s Tim Hammond, who retired to spend more time with his young family.

No Liberal candidate is contesting the seat that was won by Mr Hammond in 2016 with a 3.3 per cent margin.

Labor’s candidate for Perth Patrick Gorman at a pre-poll station this week. Photo: AAP

Labor candidate Patrick Gorman, former Kevin Rudd staffer and WA Labor secretary, is expected to win against a field of 15 candidates.

Fremantle, Western Australia

Labor’s Josh Wilson is expected to win back the seat of Fremantle, despite resigning in May over his dual British citizenship.

The seat, held by Mr Wilson with a 7.5 per cent margin, is being contested by seven candidates. But like the seat of Perth, the Liberals have not fielded a candidate.