A Conservative MP's decision to cross the floor and join the Liberal party is "exceptionally valuable", Canadian Prime Minister Mark Carney said on Wednesday, as he looks ahead to passing his first federal budget.

Chris d'Entremont from Nova Scotia defected to the Liberals on Tuesday shortly after Carney put forward his fiscal plan, inching the Liberal government closer to a majority.

Speaking to reporters on Wednesday, d'Entremont said he left because he no longer felt represented by Conservative opposition leader Pierre Poilievre.

Poilievre and his party have criticised Carney's budget as doing little to address the cost of living while ballooning Canada's deficit.

In a statement, the Conservative party accused d'Entremont of breaking his promises to the Canadians who elected him, and of defecting due to "personal grievances" with the party.