SNP deputy leader Stewart Hosie has announced he will not stand for re-election to the post at the party's annual conference.
The MP, who has faced allegations of having an affair, said he wanted to leave the post to concentrate on his health.
In a letter to party leader Nicola Sturgeon he said: "I am writing to you firstly to apologise for any hurt and upset I have caused to friends, family and colleagues. That was never my intention.
"I am also writing to tell you of my intention not to seek re-election as Depute Leader of the SNP at this year's annual conference, giving ample time for the Party to choose a successor.
"As you know I have been admitted to hospital on three occasions in the past few years with very high blood pressure. In that regard, the stress of the intense scrutiny of my private life has been very difficult.
"I intend to concentrate on my constituents, my responsibilities at Westminster, and most importantly, my health.
"It has been a pleasure to serve under your leadership and I hope to do so for many years to come.
"I wish you, your Government and our Party every success."
Ms Sturgeon paid tribute to Mr Hosie's work as depute leader and in particular to his work on the 2015 and 2016 election manifestos.
She replied to the MP: "Thank you for your letter of earlier today advising me of your intention not to seek re-election as Depute Leader of the Party," Scotland's First Minister said.
"Your decision to make this known now will allow an election for your successor to be conducted in advance of the autumn conference.
"I want to take this opportunity to thank you for your service as Depute Leader since November 2014. During your tenure in office, amongst your many other duties, you have authored two successful election manifestos - providing the policy platform for our victories in both the 2015 General Election and the 2016 Scottish Parliament election. These are achievements you should be very proud of.
"As you step down as Depute Leader, I know you will continue to make a valuable contribution to the Party in many ways and, in particular, through your work in your constituency and as part of the Westminster group.
"I have enjoyed working with you as Depute Leader - and I look forward to continuing to work with you in the future.
"I wish you well."