The first rule of Fight Club is you do not talk about Fight Club.

That famous line from Brad Pitt's 1990s Hollywood classic is, perhaps, the most apt description of what lies ahead tonight in Wentworth's Liberal preselection battle.

The process is secretive — party rules prohibit people vying for preselection speaking publicly.

It can also be bruising — when former prime minister Malcolm Turnbull wrestled the seat from sitting MP Peter King in 2004, the stoush ended in court.

The byelection date has been set for October 20.

Tonight's battle will be played out at a sporting club in Rose Bay, the harbourside epicentre of this most affluent electorate.

Wentworth takes in leafy Sydney locales like Woollahra, Bondi and Point Piper. The seat is one of only two federation electorates that have never been won by Labor.

High-profile politicians have called it home and there is an expectation those who hold it are senior minister material.

Eight people have put their hands up — among them a glittering list of doctors, diplomats, business leaders and, of course, Liberal heavyweights.

Dave Sharma, Peter King, Mary-Lou Jarvis, Katherine O'Regan, Richard Shields, Michael Feneley, Carrington Brigham and Maxine Szramka are all in the ring.

The one who emerges victorious tonight will face the challenge of keeping the seat in Liberal hands.

There is an enormous buffer of 17.7 per cent from the last election, but things are different now.

The loss Mr Turnbull as the popular local member and the events that led to his ousting as prime minister have added an x-factor to this contest.

ABC election analyst Antony Green estimates Mr Turnbull's departure could automatically slash as much as 5 per cent off the margin.

The leadership dramas in Canberra mean a Liberal victory is no longer a given and party members at tonight's meeting are under pressure to pick a candidate who can win.

The popularity of former prime minister Malcolm Turnbull, whose resignation from Parliament triggered the Wentworth by-election, will play a significant part in the poll, according to analysts. ( ABC News: Jed Cooper )

Candidates pull out

Christine Forster, the Liberal councillor and sister of Tony Abbott, abandoned her tilt at the seat less than a week after announcing she would run, claiming her candidacy had become a "proxy for division" within the party.

Andrew Bragg, who was widely considered the frontrunner and Mr Turnbull's pick, also pulled out on Monday, saying a woman should be preselected.

Christine Forster, Tony Abbott's sister, pulled out of the race days after announcing her intention to run for preselection.

It came after allegations from federal Liberal MP Julia Banks of bullying and intimidation of woman and her decision to quit politics.

Julie Bishop, free from the shackles of cabinet ministry, also weighed in and criticised the Liberal Party's record of promoting women.

Canberra has, this week, been awash with debate over whether the party needs quotas for women.

Mr Bragg also commissioned polling that suggested a woman would increase the Liberals' chances of retaining the seat.

There are three women running for preselection: former government staffer and businesswoman Katherine O'Regan, president of the NSW Liberal Women's Council and former Turnbull staffer Mary-Lou Jarvis and rheumatologist Maxine Szramka.

The moderates are locking in their support behind Ms O'Regan.

Andrew Bragg says he wants to see more women representing the Liberal Party. ( Supplied: Andrew Bragg )

She and Mary-Lou Jarvis have previously faced off in a Liberal preselection — for Woollahra Council — and Ms Jarvis emerged victorious.

Speeches, questions to precede vote

There is also a push from powerful players for the former Australian ambassador to Israel, Dave Sharma, to win the candidacy despite him not living in the electorate.

It is understood Mr King — the former member who is giving it another shot — has reconnected with some older preselectors.

All candidates will address members tonight, which are appointed delegates from the local 19 branches as well as a random selection from the NSW Liberal's head office.

They each have eight minutes for a speech and then take 12 minutes of questions.

Voting occurs until one person earns a majority.

It is all done behind closed doors — sources have told the ABC the process will be hotly contested and have alleged some "dirty tactics" in the lead up.

And that brings us to the second rule of fight club — you do not talk about fight club.

The gloves will be off tonight.