Scottish Labour leader Anas Sarwar is expected to stand down from Holyrood to join Andy Burnham's UK Government as a business minister.
The move would see Mr Sarwar resign as Scottish Labour leader, leave the Scottish Parliament and take a seat in the House of Lords.
His departure is expected to trigger a Scottish Labour leadership contest, although no Holyrood by-election will be required as he was elected via the regional list.
During the Holyrood campaign in May, Mr Sarwar ruled out joining the Lords, saying: "No. I'm focused on being first minister of this great country."
He added: "My only commitment, my only focus, is serving my constituents in Glasgow and serving the great people of this country, if I get the honour of being first minister."
The move has attracted criticism from opposition parties. SNP deputy leader Keith Brown said: "This is a terrible look for Andy Burnham who waxed lyrical about a new politics and devolving power - he's just pulled the most undemocratic trick in the Westminster book."
Reform UK's Scotland deputy leader Thomas Kerr said: "Only weeks ago, Anas Sarwar stood before the people of Glasgow asking for their trust and insisting that his future was here in Scotland. Today, those same voters will rightly feel betrayed."