Ogmore MP Huw Irranca-Davies said in a statement: "The decision is entirely my own. It has been a privilege to serve as a Minister and Shadow Minister alongside passionate and talented colleagues, and I do not rule out a return to the frontbench in future if the opportunity arises.
"But for now I intend to play a full and constructive role in the rebuilding of the Labour party in Wales and the UK from the backbenches, speaking up as always for my constituents, putting forward ideas which will reconnect people with politics, and working for Labour success in the elections for the National Assembly for Wales next year."
Mr Irranca-Davies, who was part of Labour's DEFRA team, tells me he wanted more freedom to contribute to policy development and campaign strategy in the run-up to next year's elections - although he won't be a candidate for Cardiff Bay.
He says that in the general election people understood the difference between parliament and the assembly but also saw how they were linked on issues such as health and social care and work and welfare.
The former Wales Office and DEFRA minister says he hasn't decided who to vote for in the Labour leadership election but was struck by a comment made by a constituent during the campaign that has just ended.
A constituent told him: "You are playing some good notes but you haven't got the whole symphony yet". Whoever can get the whole symphony - as leader and deputy - will get the Irranca-Davies vote.
Would-be candidates and their teams have already been taking soundings among MPs as they seek the nominations needed to enter the contest but few Welsh Labour MPs appear ready to offer their endorsement until more candidates declare..
A Welsh MP who was a minister under Tony Blair and Gordon Brown has quit the Labour frontbench.