Premier Ben Carroll will cut the number of ministers in his cabinet in what he says is a simple demonstration of his commitment to prioritising Victorian taxpayers’ money.

Following the resignations of Jacinta Allan and her Left faction loyalists Lily D’Ambrosio and Harriet Shing last week, Mordialloc MP Tim Richardson was on Monday promoted to cabinet, bringing the number of positions from 22 to 20. The remaining two cabinet positions will remain unfilled until after the state election.

The move also ensures Labor’s dominant Left faction, which split over last Tuesday’s leadership change, does not descend into further infighting over who should fill the two vacant positions.

“It doesn’t pass the pub test for having multiple ministers signed in 12 weeks out before a campaign begins,” Carroll said on Monday. “So we’re reducing the size of the ministry as a simple measure, but a demonstration of my commitment to taxpayers’ dollars.”

While Victorian MPs receive a base salary of $219,391 a year, cabinet ministers are paid an additional $184,407 and receive $19,628 in allowances. Elevating three new ministers would also increase the workload of an already stretched Victorian public service, which must prepare extensive briefings for each new member of cabinet, and is set to enter caretaker period four weeks before the election.

Richardson’s promotion is the result of hardline bargaining from Sonya Kilkenny during Labor’s caucus meeting last week. The attorney-general initially stood against Carroll for the party leadership position, threatening to force a six-week internal campaign, before withdrawing her candidacy on the condition Richardson be given a cabinet position.

Richardson, who was with Allan in her Treasury Place office when a cross-factional delegation of MPs confronted her last week and urged her to resign, backed Kilkenny during the caucus meeting.

On Monday, after a comparatively brief meeting of caucus approved unopposed his elevation to cabinet, Richardson said Carroll and Deputy Premier Gabrielle Williams could rely on him.

“They know how much I support them, and they know that over the next 117 days, I will leave absolutely everything on the field … in my support of the premier and deputy premier,” Richardson said.

Carroll will finalise a new-look frontbench on Monday evening before cabinet meets on Tuesday morning.

The dramatic change of party leaders, along with the cabinet resignations of Allan, D’Ambrosio and Shing, has given the new premier a rare opportunity to make wholesale changes to government executive, with the major portfolios of health, education, energy and climate change all in need of new ministers heading into the November 28 election.

There is speculation Carroll will also appoint a new treasurer and finance minister on Tuesday.

Ingrid Stitt is believed to be the leading candidate for the health portfolio, which had been held by Shing. The move would potentially free up Stitt’s current special minister for state portfolio, which is likely to be responsible for the royal commission into the building industry.

Colin Brooks is also believed to be a potential replacement for Treasurer Jaclyn Symes, and Police Minister Anthony Carbines could add finance to his portfolios.

Symes, a former attorney-general, is also the minister for industrial relations and government leader in the upper house. One of Allan’s chief supporters, she handed down two budgets, returned Victoria’s finances to an operating surplus and has expressed no intention to retire from politics at the next election.

Kilkenny, who also serves as attorney-general and planning minister, is the current finance minister.

Carroll was expected to inform the ministers of their new portfolios late on Monday.

More Victorian Labor news:

• Carroll’s long run:Can the boy from Airport West outrun Andrews’ ghost?
• Building Bad:The $109 billion question that ultimately cost Jacinta Allan her career
• Suburban Rail Loop:Carroll has just weeks to decide on SRL as watershed moment looms