The SNP is to announce its new Westminster group leader later.
Three of the party’s MPs have put their name forward for the post, which became vacant when Angus Robertson lost his seat in last week’s general election.
They are Ian Blackford, Joanna Cherry and Drew Hendy – all of whom were first elected two years ago.
A fourth candidate, Edinburgh East MP Tommy Sheppard, withdrew from the contest on Tuesday, saying it was clear he did not have enough support to win.
Mr Blackford, the MP for Ross, Skye and Lochaber, is said to be the favourite to win the contest, with the result expected on Wednesday evening.
A former investment banker, he was the party’s treasurer before falling out with then-leader Alex Salmond, which resulted in Mr Blackford being suspended by the party in June 2000.
But it was announced in 2015 that Mr Blackford would be the SNP’s candidate in Ross, Skye and Lochaber in that year’s general election, which saw him defeat former Liberal Democrat leader Charles Kennedy.
He went on to hold the seat in last Thursday’s election with a majority of nearly 6,000 over the Conservatives – the second largest enjoyed by any SNP MP.
The new group leader will get to quiz Theresa May every week at Prime Minister’s Questions, making it a high-profile role.
Mr Robertson, who is also the SNP’s deputy leader, had won widespread praise for his performance at PMQs, with many political opponents commending his forensic questioning of the prime minister.
But he became one of the most high-profile SNP casualties in last week’s election when he lost his Moray seat to Conservative MSP Douglas Ross.