Tasmanian Greens MP Nick McKim has been confirmed as Christine Milne's Senate successor in Hobart.

Ms Milne said she could not be happier with her replacement and Mr McKim said he was looking forward to being a fierce advocate for Tasmanians in the Senate.

The former state Greens leader and Giddings government minister was one of nine Greens party members who stood as candidates for the casual vacancy.

An internal ballot was concluded last Friday and the result was announced by Senator Peter Whish-Wilson.

"Nick, we're going to make a dynamic duo for Tasmania and for the Senate and for the Green movement, and I'm really looking forward to working with you," he said.

Mr McKim paid tribute to Senator Milne whom he described as his political hero.

"Christine Milne has done the most awesome job over an incredibly long period of time, both in the Tasmanian Parliament and the Australian Parliament, representing the Greens, being a fierce advocate for Tasmania," he said.

"She is going to leave enormous shoes to fill but I'm looking forward to the challenge.

"The thing about challenges is you need to rise to them, and I'm really looking forward to rising to this challenge, to representing the Greens, to representing our members and voters in the Senate and to representing this fantastic state of Tasmania."

Mr McKim said he was looking forward to Tasmania being seen more as a prime international drawcard and less as the butt of Australian jokes.

"I know it's a bit of a national joke at times and they have a little national chuckle at Tasmania, but laugh while you can because Tasmania is coming for the rest of the country and we have got what the world wants and what the world more and more is willing to pay for," he said.

"Laugh while you can because you won't be laughing at Tasmania for much longer."

Mr McKim said he had "lost some bark" during his years as a cabinet minister when the Greens formed a minority government with Labor in 2010.

Many Greens voters saw the collaboration as a betrayal and in the 2014 poll the party's vote plummeted and Mr McKim stepped down as leader.

"When you're in government you do need to make tough decisions, and you always lose a bit of bark."

He said he would take a fresh perspective to Canberra.

After his success, Mr McKim said he would resign from the Tasmanian Parliament shortly, which meant his state seat would be the subject of yet another Hare Clark count back.

Tasmanian Greens won't be weaker without McKim: Milne

Senator Milne rejected suggestions that the Tasmanian Greens would be weaker in the State Parliament without Mr McKim's presence.

She said similar views expressed when Bob Brown left the Tasmanian Parliament in 1993 did not prove true and the Greens continue to have a strong party base across the country.

"What this is allowing is a new perspective to come into the Tasmanian Parliament and for Nick to bring his experience to the Australian Parliament," she said.

"Just as Bob has continued as an activist outside the Parliament, I will be an additional pair of hands outside the Parliament.

"So rather than being a weakening, what we are actually doing is moving more people in to do more and create another pair of hands at every level."

McKim's seat to be subject to count back

Mr McKim led the party from 2008 until 2014, replacing Peg Putt, and became the first Australian Green, along with Cassy O'Connor, to hold a ministry.

Senator Milne announced she was stepping down as the Australian Greens leader in May and would not recontest the next federal election.

Her retirement triggered a secretive internal electoral battle which attracted nine candidates.

More than 1,000 registered Greens party members in Tasmania were eligible to vote in the contest via post or email.

Mr McKim's challengers included Save The Tarkine activist Scott Jordan, Launceston lawyer Vanessa Bleyer, Huon Valley councillor Rosalie Woodruff and Hobart alderman Anna Reynolds.

All candidates travelled around the state to campaign for the role and the voting process took place over several weeks.

Aspiring senator Ms Woodruff is the former Greens candidate most likely to assume Mr McKim's seat.