Gunghalin-based backbencher Suzanne Orr will be the ACT's newest minister, filling the vacancy left by Meegan Fitzharris.
She was elected uncontested by Labor's caucus on Friday morning.
The left-aligned MLA, who was elected in 2016 in the seat of Yerrabi, will become the government's eighth minister.
Her appointment fills the vacancy from the resignation of former health and transport minister Meegan Fitzharris in June, who also represented the northern suburbs electorate.
Chief Minister Andrew Barr will announce Ms Orr's portfolio on Monday, although he has ruled out handing her the health or transport ministry, which were assigned to Rachel Stephen-Smith and Chris Steel in the wake of Ms Fitzharris' shock departure.
On Friday, Ms Orr, who has worked as an urban planner, dismissed suggestions that she was gunning for a portfolio in her area of expertise.
"I look forward to serving in any role the Chief Minister thinks I can best contribute to," Ms Orr said.
"I am an urban planner, but I think that it's fair to say that all ministers do not necessarily go into the field they come from in their profession.
"I think the current planning minister [Mick Gentleman] is doing a great job."
Raised in Giralang and now living in Franklin, Ms Orr described herself as a "Yerrabi girl through and through".
Her promotion to the ministry makes her Labor's most senior figure in the Gungahlin-based electorate, which extends to Hall and parts of Belconnen.
She polled 7.3 per cent of the vote in 2016, the fifth highest tally among all candidates.
The electorate is shaping as a key battleground in next year's ACT election, with Ms Fitzharris' departure raising Liberal party hopes that it can snatch a prized third seat in Yerrabi at the October ballot.
"We have a really good team here," Ms Orr said, acknowledging fellow Yerrabi Labor MLA's Michael Pettersson and Deepak-Raj Gupta.
"I look forward to leading that team."
Ms Orr cited her advocacy for Giralang Community Park and efforts to secure a "positive way forward" for a long-awaited redevelopment of the Giralang shops as the highlights of her short political career.
She promised to be a strong advocate for Labor's promise to grow the public service and keep territory assets in government hands.
Mr Barr described Ms Orr as part of a "new generation of Labor MLA's", whose promotion to cabinet marked another step in the ongoing renewal of the party.
He acknowledged the importance of having a Gungahlin-based minister in the 14-month lead in to the next territory election.
"We want our ministry and government to reflect the community that we represent," Mr Barr said.
Mr Barr was not surprised that Ms Orr was the only Labor backbencher to nominate for the vacancy, saying that "from time to time ... there is clear agreement".
He confirmed Labor would take the current ministerial lineup to the next election, but forecast future promotions for the party's remaining backbenchers - Mr Petterson, Mr Gupta, Bec Cody and Tara Cheyne.
"Each one of those non-executive members can and will serve in the executive of our party," Mr Barr said.
"They all have that capability."