Caroline Flint has left the Government after resigning as Europe Minister, Gordon Brown announced tonight.
She is to be replaced by Glenys Kinnock, the wife of ex-Labour leader Neil Kinnock, the Prime Minister said.
Mrs Kinnock will join the House of Lords immediately, he added.
Ms Flint today berated Gordon Brown for treating her as "female window dressing''.
In her resignation letter Ms Flint said Mr Brown was operating a "two-tier Government: your inner circle and the remainder of the Cabinet''.
Only last night Ms Flint insisted she was "very proud'' to be a member of Mr Brown's Government and would not be leaving it.
But Mr Brown told a press conference this evening that she was in fact stepping down after refusing an enhanced role as Europe Minister.
He said she “was and has been a very good minister”, adding: “I asked Caroline if she would take on the job attending the Cabinet so she would be present at every Cabinet meeting.
“Unfortunately she didn’t see it that way and that’s where it’s left.”
Ms Flint’s is the latest of a spate of ministerial resignations in recent days - which she vowed last night not to join.
Speaking to the BBC, she said: “I am staying in the Government.
“I have spent my entire ministerial career for six years now serving Tony Blair and Gordon Brown, and I am very proud to be in a Labour Government and very proud to be part of Gordon Brown’s Government.”