Ms Garrett will take the seat held by Daniel Mulino, with the Eastern Victorian MP going to federal parliament in the newly created seat of Fraser in Melbourne’s north-west.

It is understood the deal, brokered by Ms Garrett’s factional ally Adem Somyurek, comes with the understanding that Mr Mulino’s union, the SDA, will be found another seat in State Parliament in return for its support.

Ms Garrett, who announced in September that she would not contest her seat of Brunswick in November's state election, will now take the number 1 spot on Labor's ticket in Eastern Victoria with Harriet Shing at number 2.

Mr Mulino must contest and win Fraser, which is expected to be very safe Labor territory, at the next federal election and the party has not yet worked out the details or the timing of the seats switch, but the arrangement does not mean that Brunswick voters will face a byelection.

The agreement will now go to Labor's national executive, which meets on Tuesday morning, for endorsement.

A last-ditch attempt was made Monday by the United Firefighters Union, Ms Garrett’s bitter foes, to derail the deal with union leader Peter Marshall again trying to persuade senior figures in the party that Ms Garrett should not be given a parliamentary seat because she had acted against “Labor values” during her time in the ministry.

Lawyers for the union wrote to the state’s anti-corruption agency, the IBAC, on Monday asking it to investigate allegations, first raised in 2016 and denied by Ms Garrett, that she acted improperly in offering promotions to a Melbourne firefighter who had helped to get her elected.

The Brunswick MP could not be contacted for comment.

But while Ms Garrett’s career has been thrown a lifeline, Victorian Labor Senator Gavin Marshall has emerged as a casualty of the factional tussle within his party over federal preselections.

The political veteran, who was contacted on Monday for comment, has been dropped down the party’s upper house ticket by his left faction, in defiance of Opposition Leader Bill Shorten’s orders that sitting members are not to be dumped.

Senator Marshall’s winnable spot on Labor’s Senate ticket at the next election will be given instead to United Voice union official Jess Walsh.

The idea of Mr Mulino going to Canberra had been quashed by his union, who feared a loss of numbers and power in the Labor’s state caucus, but was revived in recent days after a backlash against a plan to install St Albans MP Natalie Suleyman in Fraser.

Many in the party were aghast at the idea of parachuting Ms Suleyman, who has a controversial past as mayor of Brimbank.

The race to contest the seat of Jagajaga in Melbourne’s north-east, vacated by former federal minister Jenny Macklin, has been won by former Macklin staffer Kate Thwaites who edged out local activist Sonja Terpstra.

Macnamara, formerly Melbourne Ports, looks set to be contested by Josh Burns, a former staffer for retiring MP Michael Danby, amid allegations of dirty tricks and a stacked electorate meeting.

Supporters of rival candidate Mary Delahunty say they were physically barred by security guards from entering a meeting of local party members last week which endorsed Mr Burns as its preferred candidate and have taken their complaints to the party authorities.

Cr Delahunty says she is undeterred and will nominate to be considered by the National Executive as the candidate for the seat.