An Independent MP is joining the New Democratic Party, saying she was also in negotiations to become a Liberal but things fell apart when Justin Trudeau would not meet with her.

Maria Mourani, who began her federal political career as a member of the Bloc Québécois, signed an NDP membership card Wednesday with Leader Thomas Mulcair at her side. Despite her new affiliation, she will continue to sit as an Independent until the next election to conform with an NDP prohibition against floor crossing.

The endorsement of the former Bloquiste was a boost for Mr. Mulcair, whose New Democrats fared miserably in two by-elections this week and have been struggling in the polls for more than a year.

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But the NDP and the Liberals have different stories to tell about how Ms. Mourani came by her new political stripe – a squabble that has become one more point of friction between two parties vying for the centre-left vote in the 2015 election.

Ms. Mourani was ejected from the Bloc in September, 2013, over her condemnation of a Parti Québécois proposal to prevent provincial government workers from wearing visible religious symbols. She says she was very quickly approached by Liberals and then began a prolonged series of talks with the Liberals. "And at the end of my discussions, so many discussions, I realized this party was not for me."

Her decision, she said, was based partly on Mr. Trudeau's unwillingness to meet with her. "I need to talk with the leader if I want to go to the party," Ms. Mourani said. "I have to know if we have connections, if we share the same ideas of politics, of values. But [they said] 'it's not important, Maria, to meet him.' How come?"

Mr. Trudeau, on the other hand, said it was Ms. Mourani who came "a number of times" to the Liberals to express an interest in joining his team. "We indicated that there was a process," he said. "We have open nominations. And it never got far enough along for me to actually sit down and meet with her."

In welcoming Ms. Mourani to his fold, Mr. Mulcair said the Quebec MP is to be respected for standing up for her convictions. Since leaving the Bloc, she has publicly abandoned Quebec sovereignty, stating that Canada offers the best protection for minority rights in her home province.

But the New Democrats have a policy against floor crossing and even introduced a bill, which failed on second reading, to prohibit MPs from changing their banners after they are elected.

Mr. Mulcair said she will have to seek the nomination in her riding and then get elected as a New Democrat before she can sit with the NDP. Ms. Mourani said she will announce in the coming weeks whether she plans to do that.

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When asked how it helps people of the Montreal district of Ahuntsic to have Ms. Mourani sitting as an Independent rather than as a New Democrat, Mr. Mulcair chose not to directly answer the question. "As you know, the NDP has a long-standing position that we find is an important position of principle," he said, "It's a position of electoral ethics. If you get elected for one party, you can't just in midstream move to another."