A prominent Liberal Party member with familial ties to Leader Justin Trudeau has defected to the Green Party.

Deborah Coyne, former Liberal leadership candidate and a constitutional lawyer, announced Thursday she will serve as senior policy advisor to Leader Elizabeth May.

“I look forward to joining Elizabeth to help make the Green Party the first choice for voters who are disillusioned with the existing state of politics in Canada,” Coyne said.

May welcomed Coyne to the smallest federal party in the House of Commons.

“Deborah’s thoughtful approach to one Canada for all Canadians complements the vision of the Green Party of Canada,” May said. “I look forward to Deborah sharing her practical and policy experience on a wide range of issues in her new role as a senior policy advisor to the Leader.”

Coyne is Trudeau’s half-sister’s mother, and she ran unsuccessfully against him in the last Liberal leadership race.

She aid the Green Party promotes a “more civil, constructive and collaborative governance.”

She would not say whether she will run for the Green Party in the next election.