Dimitri Soudas helped broker the defection of his fiancée and former Conservative MP Eve Adams to the Liberal Party, in a stunning move for a long-time Harper loyalist and former high-ranking Conservative official.

Ms. Adams is now exploring the possibility of running in the Toronto-area riding of Eglinton-Lawrence against Finance Minister Joe Oliver. Party sources said this is why she quickly attacked the government's income-splitting proposal, despite past support for the matter, in her first public comments as a Liberal MP.

Mr. Soudas was one of the most partisan and loyal aides to Prime Minister Stephen Harper for more than a decade. But he was forced out as executive director of the Conservative Party over his involvement in Ms. Adams's messy nomination battle in Oakville North-Burlington last year, and he is now expected to become a Liberal member.

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Ms. Adams was forced to quit that nomination race over allegations of "misconduct." The party's internal review is expected to look into allegations that she received unfair advantages and that she verbally abused party members during a March 19 board meeting of the Conservative Oakville North-Burlington riding association.

As part of repeated efforts to find a riding, Ms. Adams made a plea directly to Mr. Harper last month in a Mississauga hotel. Only three people were in the room: the Prime Minister, Ms. Adams and a Conservative staff member. Mr. Harper declined to intervene, saying it was up to the Conservative Party's national council to decide the matter. "He told her he doesn't get involved in nominations," a source said. Mr. Harper also made a point of saying he knew Mr. Soudas was still supporting the MP. "He indicated to her that he was aware that Dimitri was downstairs" in the hotel, the source said.

Ms. Adams was finally told by the Conservatives on Jan. 29 that she would not be allowed to run anywhere for the party, Conservative sources said. Ms. Adams said the episode sparked a period of "soul searching," at which point she reached out to the Liberal Party and decided to jump ship. After 25 years as a Conservative, she appeared alongside Liberal Leader Justin Trudeau on Monday, unleashing a series of attacks against the Prime Minister's leadership style.

Sources said Mr. Soudas was involved in the early discussions that led to Ms. Adams's floor-crossing, using his past working relationship with senior Liberal officials from his days in the Prime Minister's Office. However, sources added Ms. Adams was solely in charge of the more recent discussions with Mr. Trudeau and his team. Mr. Soudas could not be reached for comment, but he offered his full support to Ms. Adams on social media.

Some Liberals are hoping Mr. Soudas will provide them with munitions against the Conservative Party. However, a senior aide to Mr. Trudeau, Gerald Butts, said Mr. Soudas's role would be to "put up lawn signs" on Ms. Adams's behalf, and the Liberal Party insisted that he would have "no formal role" in the national campaign.

At her news conference, Ms. Adams praised Mr. Trudeau's positive and optimistic leadership, which she contrasted to the Prime Minister's style of politics.

"I want to work with someone who inspires, not with fear-mongers and bullies," she said.

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She slammed the Conservative government's decision to adopt income-splitting for families with children, saying it favours the richest of Canadian families.

She ran under the promise to enact the policy in 2011, but said the numbers hadn't been crunched at the time, adding the late former finance minister Jim Flaherty also went on to express doubts about the policy.

"A widow wouldn't benefit, a single mom wouldn't benefit from this," she said. "There is a social conservatism to it, but more importantly, this is profoundly unfair to the middle class." Over all, she said she had not "felt at home in the Conservative Party for many, many years," pointing repeatedly to the Liberal Party's clear support for abortion rights as she explained her move.

(What is income-splitting? Read The Globe's easy explanation)

However, Conservative Party sources said Ms. Adams repeatedly inquired about the chances of returning to the race in Oakville North-Burlington, where she had first tried to run.

"She informally tested the waters a number of times over the course of the last six months about Oakville and the answer was an unequivocal 'no,'" a Conservative source said.

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A subsequent request to run in Mississauga-Malton was rejected by Conservative Party president John Walsh in a Jan. 29 letter that made it clear she would not be allowed to carry the Tory banner in 2015.

Mr. Trudeau praised Ms. Adams for her hard work at the constituency level and her past career in municipal politics. He added that in order to win the next election, the Liberal Party will need to attract Conservative voters.

"One of the keys for the Liberal Party to win the next election is to convince a lot of people who voted for different parties in the last election to vote for this party now, and when we can showcase that people of all different political stripes are turning to the Liberal Party as a strong and capable, better government, this is what we are most proud of," Mr. Trudeau said.