Glasgow MP Alison Thewliss officially announced she would run for the position on Saturday night - saying that she would be a "clear contrast" to the "two men shouting at each [other] across the dispatch box".
Up until that point Stephen Flynn had been widely tipped to replace Blackford but it wasn't until Sunday that the Aberdeen South MP officially announced his candidacy.
While making his bid, Flynn said: "I want to see a Scotland where opportunity exists for all, where we have the powers to combat poverty and to create a green energy revolution."
It is understood that Flynn's bid was proposed by Stewart Hosie and seconded by Amy Callaghan. It had previously been reported that he had the support of around 30 MPs.
Meanwhile, Thewliss was nominated by Dundee MP Chris Law and has the public support of Perth MP Pete Wishart and Stewart McDonald, MP for Glasgow South.
Cumbernauld, Kilsyth and Kirkintilloch East MP Stuart McDonald will be her running mate.
The announcement of the winner of the vote is expected to be made on Tuesday evening.
In the meantime, vote in the poll below to have your say on who should be the SNP's next Westminster leader.