"I envisage it will be some time next week and he will present that resignation to the Speaker, as is the process."

She said the Speaker would be in touch with the Electoral Commission to set a date for the byelection, which would see Wagga Wagga voters go to the polls twice in a span of months with the next general election on March 23, 2019.

"As frustrating as it is for everybody, it's the right thing to do," Ms Berejiklian said.

"I think the public would not have accepted it, had we held the seat open until March next year. I do not fear a byelection. The people of Wagga should be heard."

Ms Berejiklian said she had also spoken to Deputy Premier and Nationals Leader John Barilaro and a decision had been made that the Liberals would run a candidate in the byelection and that the Nationals would not.

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"The Liberal Party has held that seat for half a century and the Liberal Party has opened nominations," she said.

Many senior Nationals had been agitating to contest the regional seat, and under the Coalition agreement a byelection was the only time they could do that.

But Mr Barilaro on Saturday told the Herald he was happy for the Liberals to run again in the seat.

"It is a Liberal seat and they have every right to run," he said. The Nationals have no interest in three-cornered contests. History shows in NSW that three-cornered contests are not good for the Coalition."

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Labor has already announced it would contest the byelection with local councillor Dan Hayes, who ran at the 2015 general election, the party's candidate.

This month, the Independent Commission Against Corruption heard secret recordings of telephone conversations in which Mr Maguire admitted trying to earn payments by setting property developers up with investors, particularly large Chinese firms.

Following the explosive evidence at the ICAC, Mr Maguire moved to the crossbench after resigning as a parliamentary secretary and quitting the parliamentary Liberal Party.

Earlier this week, he released a video statement saying he would remain in Parliament.

"I won't resign. I'm not going to resign," he said on Monday.

"I've removed myself from the Liberal Party. I've resigned from the party only, but I won't resign as a member of Parliament."

On Wednesday, Labor said it would use rare parliamentary powers to try to expel the Wagga Wagga MP from Parliament when it resumed on August 7.

Opposition Leader Luke Foley said on Saturday the only reason Mr Maguire was now leaving parliament was because Labor was moving to expel him.

“The Premier should have moved to force him out the day the phone tap was played at the ICAC hearing but she wanted to avoid a byelection in a Liberal seat,” Mr Foley said.

Asked on Saturday why Mr Maguire had changed his mind on staying until March 2019, Ms Berejiklian said it was a "a matter for him".