Former Greens leader Christine Milne had been considering her future for six months before deciding to quit, and held discussions about her exit with Greens Party founder Bob Brown.
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Fairfax Media understands new leader Richard Di Natale, former deputy Adam Bandt, and immigration spokeswoman Sarah Hanson-Young led the push for a leadership change in the party.
Mr Bandt and Senator Milne had had a strained relationship for some time, while Senator Hanson-Young had challenged Senator Milne for the deputy leader's role as far back as 2010.
Some Greens, angry at how just one-hour's notice was given for the leadership vote, believe that if Mr Bandt had faced Senator Di Natale in a ballot, the result could have been as close as 6-5 or 7-4 in the 11-member partyroom.
While Senator Milne's decision to resign surprised many, she had discussed her future with family, friends, former staff and other members of the party in the lead-up to the announcement.
The message was clear in many of those conversations. Senator Milne was told she needed to decide sooner, rather than later, about whether she would stand at the next election.
A push for generational change was gathering pace.
At 10am on Wednesday, when the 11 Greens MPs met, some in the partyroom expected the meeting to focus on pre-budget tactics and strategy.
Instead, Senator Milne announced her plan to go and spoke for about 30 minutes about her legacy and the party's future.
At around 10.30am she announced a snap vote for 11.30am, a rapid resolution that has angered some colleagues and party members.
Some members insist that Senator Di Natale, and Senators Larissa Waters and Scott Ludlam - who were elected co-deputy leaders, were tipped off ahead of time by Senator Milne to spoil Mr Bandt's chances.
Senator Milne and Senator Di Natale have repeatedly refused to say whether or not that is true, however the new leader did confirm that the change of leadership had been on his radar for some time.
"I was talking to Lucy [his wife] about this six months ago because, you know, I might not be from a political background but I'm smart enough to know when something could happen," he told reporters on Wednesday.
Mr Bandt was the only other Greens MP to make calls seeking support from colleagues for the leadership.
But Senator Di Natale began the contest with a solid bloc of five votes in the 11-member partyroom - senators Milne, Ludlam, Waters and Rachel Siewert - and the writing was on the wall.
Some members of the party say Senator Di Natale also knew he could rely on the support of either or both South Australian senators, Penny Wright and Sarah Hanson-Young, enough to get him the six votes to get him over the line.
And so Mr Bandt, who was likely able to rely on the support of NSW senator Lee Rhiannon and possibly senators Peter Whish-Wilson and Janet Rice, decided not to force a contest.
Senator Di Natale was elected unopposed, as were senators Waters and Ludlam.
Afterwards, Mr Bandt congratulated the new leadership team, signalled plans to lead the charge to win more lower house federal seats and said he wanted to focus on the birth of his first child, due in a few weeks.
But as one Greens MP told Fairfax Media, "the [leadership] conversations didn't get far. It was clear that Adam didn't have support and that was explained to him. It was brutal for him but he has been gracious."
The rapid vote and switch to Senator Di Natale has angered some Greens MPs; "even those of us who would have voted for him", says another Greens MP.
Party members say it will lead to a renewed push at next week's Greens National Council meeting for the party to move to a model that would see party members directly elect the leader, rather than MPs.
As one put it to Fairfax Media: "we are behind Labor on this issue."
Senator Di Natale confirmed on Wednesday that a reshuffle of portfolios will now take place in the partyroom.
The new leader is said to be open to a change of structure that would see the party appoint a treasury spokesperson for the first time.
Until now, the party leader had held the economic portfolio but the change would be a tactical move designed to position the Greens more prominently in debates about the economy.
After the ballot and change of leader, Greens MPs, staff and family gathered at Canberra's Hotel Realm to drink, talk, commiserate and celebrate.
From now, the Greens will rise or fall on the shoulders of senators Di Natale, Waters and Ludlam.
