And just like that, after 12 years in politics the former ACT opposition leader officially became a former member of the ACT Legislative Assembly.

"I'm looking forward to a new chapter, whilst I am not sure what's next I do know that it's time for a change," Mr Coe said.

"With this change for me and my family also comes an opportunity for renewal for the Canberra Liberals."

Mr Coe had previously announced his intention to resign in January after he conceded he no longer had the drive to fully commit to job following the Liberals election defeat in October.

Over the past two months, Mr Coe hasn't second guessed his decision.

"I thought there would be some regret or second thoughts along the way but in actual fact as time has gone on since I made that announcement back in January I really have been reaffirmed it is the right thing to do. It's time for a change," he said.

Attention will now turn to Mr Coe's replacement. The former Liberal leader's exit has triggered a countback of votes in the Gungahlin-based seat of Yerrabi.

It is widely expected that former Liberal MLA James Milligan will be re-elected to the Assembly but leader Elizabeth Lee would not speculate as all three Liberal candidates from the 2020 election had put their hand up to fill the vacancy created by Mr Coe.

ACT Liberal Party director Josh Manuatu confirmed that Mr Milligan, Dr Krishna Nadimpalli and Jacob Vadakkedathu have all nominated.

Mr Milligan was elected to the Legislative Assembly in 2016 but lost his seat at last year's election after he was outpolled by fellow Liberal Leanne Castley.

It will be another two weeks before Mr Coe's replacement is known. The countback will take place on March 25, with the result to be revealed the following day.

Any candidate who stood for Yerrabi at the 2020 election is eligible to take part in the countback.

Under the territory's electoral act, 10 days notice must be given for candidates to nominate, ACT electoral commissioner Damian Cantwell will put out a notice on Monday.

"It is intended to give the candidates who were unsuccessful in Yerrabi time to consider whether they would wish to recontest the seat of Yerrabi and indeed make themselves available to do so," he said.

"[The countback] is entirely up to expression of the will of the people as recorded by the votes in October 2020."

Ms Lee will also have to undertake a reshuffle with key portfolios including shadow treasurer and planning up for grabs.

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"There's no doubt that the Canberra Liberals will miss Alistair," she said.

"Of course when someone who is the calibre of Alistair leaves the team it leaves a big hole in terms of experience and expertise but we're also very fortunate with the diversity that we have around our party room.

"There is no doubt that my mind has turned and will now more so to the reshuffle and that will be taken into consideration. There's a lot of talent around the room and I'll take my time in determining and discussing with my colleagues what the shape of the party will look like in the future."

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