NSW byelections to be first big test for Dominic Perrottet and Chris Minns. Here’s what to look for

After almost 11 years of Coalition dominance in New South Wales, could Labor be about to mount its comeback?

Saturday's byelections in four New South Wales state electorates are likely to have wide-ranging impacts.

The worst case scenario for the premier, Dominic Perrottet, would see the state government lose its stable majority in the lower house of parliament. More likely, though, is that these byelections could set the tone for next year's state election.

The Coalition is set to become the longest-serving conservative government in modern NSW history in March, when it exceeds the 11 years it spent in power from 1965 until 1976.

Only one government in the last half century has lasted more than 12 years - the last Labor government, which served from 1995-2011.

Winning a fourth election is historically difficult, and Saturday's byelections will provide valuable insights into whether the Coalition is beginning to be weighed down by history.

All four byelections were triggered by the resignations of senior members of the parliament:

With both the government and opposition changing leaders in the past year, we don't have much polling data to guide how Perrottet and Labor's Chris Minns are performing, so these byelections are their first major tests.

Labor is challenging the government in two of their seats: the neighbouring electorates of Bega and Monaro. Bega covers the southern NSW coast from Batemans Bay to the Victorian border, while Monaro covers inland areas between Canberra and the border, including Queanbeyan and the Snowy Mountains.

Both seats are currently on healthy margins, but Monaro was Labor-held from 2003 to 2011, and Barilaro only held the seat by small margins in 2011 and 2015, before building up an 11.6% margin in 2019. Bega has been held by the Liberal party continuously since its creation in 1988, but was a marginal Liberal seat during the last Labor government, and Constance's margin was whittled down to 6.9% in 2019.

Both seats had prominent local members who were perceived to have strong personal votes, and their absence could provide an opening for Labor to win either seat.

Win or lose, if Labor can gain large swings in both seats it will be seen as a strong result, with implications for the March 2023 state election. Minns will be evaluated more seriously as a potential premier, and there will be an expectation that Labor can win.

For the government, the loss of either seat would make its position more precarious in the Legislative Assembly, although it should be able to serve out the remainder of this term. The government now holds 46 of the 93 seats, including those up for election tomorrow, plus two ex-Liberal independents who reliably vote with the government. The loss of two seats would see their working majority lost, although they would have a number of options on the crossbench to find the missing vote when needed.

Labor is also defending the electorate of Strathfield, where McKay's resignation opened up a seat that Labor lost in 2011 before regaining in 2015.

Labor holds Strathfield by just 5%, and is facing a challenge from the Liberal party. If Labor is in a stronger position in New South Wales you'd expect them to comfortably win here, but the seat is marginal and both parties are taking it seriously.

Labor is also facing a challenge from former Sydney Morning Herald columnist Elizabeth Farrelly, who was briefly a Labor member before resigning to contest the seat as an independent. Farrelly is not recommending preferences to Labor despite her recent political history, and may peel votes off both major parties.

Willoughby would traditionally be considered a safe Liberal seat, and Labor is sitting out this contest accordingly. Independents have been popping up all over northern Sydney recently to contest the upcoming federal election, and there is an independent candidate running a similar campaign in Willoughby. This seat will most likely stay in Liberal hands, but it will be worth watching.

In the absence of detailed polling, these results will likely shape public perceptions of how next year's state election is likely to turn out. If Labor wins Bega or Monaro, the Coalition government will look shaky and be in a weak position heading in to next year. If Labor gains substantial swings but does not gain seats, it will still suggest that the next election will be competitive and that either side could win.

Beyond perceptions, a change in any of these seats will have a practical impact on the next election. Labor needs to gain 10 seats to win a majority - a gain in Bega or Monaro reduces the task for next March. The Coalition won 48 seats in 2019 and lost a seat to a redistribution. They need to hold all the seats they now hold to regain a majority. Losing Bega or Monaro means they need to make gains to win a majority.

Don't expect a result to be called quickly, however. The NSW electoral commission has taken the unprecedented step of sending postal ballots to every voter. This appears to have reduced the traditional late surge in pre-poll voting and may well slow down the calling of the results, with postal votes not due to be counted until next week.