White broke down on Wednesday morning when telling his ACT Brumbies teammates of his impending move to French club Montpellier, unable to finish a pre-prepared speech to detail why he was leaving.

The tenacious No. 9 admits the fear of being overlooked for World Cup selection played on his mind before he committed to a three-year deal, believed to be worth more than $500,000 a season.

But the 24-year-old insists it's the right time to make the move and he is poised to reunite with former Brumbies coach Jake White and captain Ben Mowen in the south of France.

Less than five months ago White was Australia's first-choice scrum half, but he dropped to third in the pecking order behind Nick Phipps and Will Genia when Michael Cheika took the Wallabies coaching reins.

"I want to go to the World Cup more than ever, the ultimate dream is winning a World Cup," White said.

"I hope it doesn't affect my position, I haven't spoken to [Cheika]. I'm sure he'll pick the best team to win it.

"My plan is to play the best footy I can down here and hopefully that's rewarded and my decision doesn't impede picking the best man for the job. I think he will pick the best squad regardless of where they are going after the World Cup."

Brumbies coach Stephen Larkham has backed White to retain the vice-captain role he was given last week, declaring White as one of the "top two scrumhalves in the world".

"He'll keep his leadership role in the team. The key is to put the right guys in those positions and Whitey will give 100 per cent to this team," Larkham said.

"He's passionate about the Brumbies and I've got absolutely no doubt he will lead in an outstanding manner this year."

White joins a concerning list of players who have already revealed their intentions to start lucrative deals abroad after the World Cup.

But while Adam Ashley-Cooper, James Horwill and Sekope Kepu are Test veterans, White is just starting his international career and has sacrificed the chance to add to his 19 Wallabies caps to move to France.

It's understood White was close to signing with a French club last year before re-committing to the Brumbies.

When Jake White took over at Montpellier, he made Nic White a prime recruiting target and the offer to reunite was too good to refuse.

"It was incredibly tough, I didn't take it lightly. Telling the boys was one of the toughest things I've done, I've made the decision now and I've got to back it," White said.

"The timing of my career and I'm not sure how often these opportunities will come along. I feel I was in a good position to make it a place I want to go to.

"It's a good time after the World Cup to get out and see what rugby has to offer. I want to make the most of it while I can.

"I wanted to tell the Brumbies before round one, knocking it on the head was the right thing for the team."

White was contracted to stay with the Brumbies and the ARU until the end of 2016, but decided not to take up the option to play beyond the end of the year.

White says his focus is leaving Australia on a high - first with a Super Rugby title with the Brumbies and then chasing World Cup glory with the Wallabies.

He played just one Test on the spring tour of Europe just months after being in the starting side.

"I feel like a weight's been lifted off my shoulders ... I've definitely got extra motivation knowing this is my last season here. I want to go out with a title, I don't want to leave any stone unturned.

"I don't see this as closing the door on Australia, I can't predict where I will be in two or three years' time."