Ian Blackford has said he will quit as the SNP's leader at Westminster after more than five years to make way for "fresh leadership".
The Ross, Skye and Lochaber MP announced he would step down amid reports of attempts to oust him.
In a statement, he said: "I have today informed SNP MPs that I will not be re-standing as leader of the Westminster parliamentary group at our AGM next week.
"After more than five years in the role, now is the right time for fresh leadership at Westminster as we head towards a general election and the next steps in winning Scotland’s independence."
He will continue to serve as an MP.
Only last week, Mr Blackford told the Scotsman he "looked forward" to putting himself forward for re-election and he hoped to be "the MP which leads the SNP group out of Westminster for the last time".
Fellow SNP MP Stephen Flynn is being tipped to succeed him - despite denying recent reports he was seeking to challenge Mr Blackford for the top job.
The Aberdeen South MP, who is the party's energy spokesman, recently tweeted: "As much as I love seeing photos from the days when I was still clinging on to some hair, I can confirm I’ve no intention of standing."
One SNP MP told the Mirror that the succession would not be "some kind of blood bath" and Mr Blackford would support whoever leads the party in London.
They added: "Renewal is not always a bad thing."
In a sign of some of the tensions within the party, the SNP's Joanna Cherry pointedly tweeted that she welcomed a chance to choose a new leader.
Ms Cherry, who has been at odds with Nicola Sturgeon in recent years, said: "I'm pleased to hear this. It's time for fresh leadership & tolerance of debate & diverse viewpoints.
"I hope the SNP Westminster group will be now be left to choose our new leader without outside interference & in accordance with our standing orders."
Ms Sturgeon paid tribute to Mr Blackford's leadership during a time of political turmoil.
"I would like to place on record my thanks for Ian's diligence, tenacity, friendship and loyalty in his time as group leader," she said.
"He will continue to play an important role as constituency MP for Ross, Skye and Lochaber, and I have also asked him to take on a role as part of the wider SNP team preparing the case for independence."
The First Minister added: "I look forward to working with Ian's successor as group leader at Westminster, as we continue to make the case for the people of Scotland to have a democratic choice on the country's future."
