Peter Hain has announced he will stand down as the Labour MP for Neath at next year's general election.
The former Cabinet minister said he had "decided to draw stumps" on his Commons career following a series of discussions with Ed Miliband.
Mr Miliband praised the Neath MP for his integrity, wisdom and tireless work for the country and said he would be sorely missed.
During his lengthy career, he served in the cabinet under Tony Blair and Gordon Brown, with stints as Welsh secretary, Northern Ireland secretary, work and pensions secretary and leader of the Commons.
Mr Hain had been reselected to fight for the 2015 election for Neath, but said he would now find 'new ways' to be involved in politics.
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Official figures show areas of Caerphilly, Rhyl, Wrexham, Rhondda Cynon Taf and Bridgend to be the most deprived in Wales.