Mark Parton takes over the Canberra Liberals after Leanne Castley and her deputy Jeremy Hanson resigned on Monday, saying it will give the Liberals the best shot at governing in 2028.
Ms Castley rolled then-Liberal leader Elizabeth Lee following the 2024 election defeat in October.
"In the spirit of ensuring a genuine fresh start for the new team, we will not be commenting publicly on the circumstances that have led to this decision," Ms Castley said in a statement on Monday.
The Canberra Liberals have been in the political wilderness for more than two decades, and will have been in opposition for some 27 years when the 2028 election comes around.
The more conservative Deborah Morris assumes the mantle of deputy.
"It's vital that we continue to strengthen the cohesion within our party," Mr Parton said in a statement.
"By encouraging open dialogue, valuing diverse perspectives, and finding common ground, we can reinforce our shared purpose."
The Canberra Liberals have been plagued by accusations members are too conservative for the progressive ACT, where it has no federal representatives.
Ms Castley had recently attempted to kick Ms Lee and moderate colleague Peter Cain out of the party for crossing the floor in the ACT Legislative Assembly - which backbench Liberals are allowed to do - to vote for more parliamentary sitting days.
Ms Lee and Mr Cain were booted from the party room by Ms Castley after they voted alongside the Greens to add an extra sitting week in 2026, while the Liberals voted with Labor to maintain the planned 12 weeks.
The Greens' motion ultimately failed.
Ms Lee said she was perplexed at the move to dispel her because it was party convention that MPs could cross the floor, and Ms Castley offered no explanation, repeating it was an internal party matter.
Labor holds 10 seats in the 25-seat assembly, with four Greens and two independents making up the cross bench.
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