Nine candidates put their hand up to replace Senator Milne, who stepped down from the leadership and announced her retirement earlier this year.

Former Tasmanian Greens leader Nick McKim is heavily favoured to have won the contest from a field that also included Save the Tarkine leader Scott Jordan and Launceston lawyer Vanessa Bleyer.

Also in the race are epidemiologist Rosalie Woodruff, Hobart alderman Anna Reynolds and West Coast resident Matthew Ryan-Sykes.

A meeting of the party's state executive ratified the ballot result on Monday evening, but the result will not be publicly confirmed until Thursday.

The announcement will be attended by Senator Milne, fellow Tasmanian Greens Senator Peter Whish-Wilson and the successful candidate.

A great deal of secrecy surrounds the ballot, with three candidates not publicly announced, and scrutineers forced to sign confidentiality agreements about the result.

The party's nomination would have to be formally confirmed by state Parliament, and would face the people at the next federal election, due next year.

If Mr McKim were successful, it would mean a countback in his state electorate of Franklin, which would likely be won by Dr Woodruff.

Mr McKim is on leave and could not be contacted on Monday.

The party has already confirmed that Carol Beaumont will contest the seat of Bass at the next federal election, while Martine Delaney will represent the party in Franklin.

The preselection process for the seats of Lyons, Braddon and Denison will start shortly.