Former Greens leader Christine Milne has paid tribute to her party colleagues in her last speech to the Senate.

Senator Milne announced her resignation as Greens leader last month, and said she would not be recontesting her position at the next federal election.

Party staff have told the ABC she did not want to make an official valedictory speech, and wanted to have a more low-key exit from political life.

Senator Milne told the chamber the strength of the Greens is found at its roots in activism.

"It is a case of striving to seek to find, and not to yield, or as Peter Cundall in Tasmania would say, 'we will never ever give up'," she said.

"And that is essentially where the Greens come from, and it's where I come from. I'm an activist.

"I'm not leaving politics, I'm not leaving the Greens, I'm leaving political representation, but for the Greens, activism is everything in and out of the Parliament.

"And I will be there as an activist, purple stockings and more dangerous than ever."

Acting Government leader in the Senate Attorney-General George Brandis said Senator Milne's final speech was an occasion all sides of politics should mark.

"On the occasion of someone's farewell, it is appropriate to put to one side political differences, perhaps even bitter differences of political opinion and to acknowledge their service," he said.

"You are one of the relatively few Australians to give your life to public affairs and to the causes about which you felt passionate, and for that you should be respected and thanked and admired.

"I've always found it possible to respect people whose points of view I profoundly disagree with, and I would put you in that category.

"What I respect is the fact that you have brought a passion and a commitment to the prosecution of your beliefs, and you've been very successful."

Labor's Senate leader, Penny Wong, noted in her tribute Senator Milne was one of the few women to have led a political party.

"Your activism, your struggle will not diminish in your departure from this place," Senator Wong said.

"I also note there are not many women who get to lead a political party, and I salute you for being a woman who has led your party in this place."