Former prime minister Gordon Brown is expected to announce later that he is standing down as an MP, according to sources.
It is understood that the 63-year-old will announce in a speech in his Kirkcaldy constituency tonight that he will step down at the general election in May, after playing a key role in the Scottish independence referendum campaign this year.
The Labour MP has focused on charity work and his role as United Nations special envoy for global education since his resignation as prime minister in 2010.
Mr Brown was first elected to Parliament in 1983, was chancellor from 1997 to 2007 and then prime minister from 2007 to 2010.
His last-minute intervention in the referendum debate was widely credited with helping the pro-union Better Together campaign to victory.
A timetable he championed for devolving more powers to Scotland was later endorsed by the three UK party leaders in their vow for greater autonomy for the Scottish Parliament in the event of a No vote.
A series of impassioned speeches, culminating in an eve-of-poll rallying cry in Glasgow, was also widely praised.
Mr Brown had been tipped to stand for the Scottish Labour leadership following the shock resignation of Johann Lamont, but instead made clear he had no intention of returning to frontline politics.
He won the Kirkcaldy and Cowdenbeath seat with a majority of more than 23,000 in the last election.
Former Labour chancellor Alistair Darling has also announced that he is to stand down as an MP at the next general election in the wake of the referendum.