Mr Browne said he would support the next Labour candidate for his seat
Former defence secretary Des Browne has announced he is to quit the House of Commons at the next general election.
Mr Browne, who also served as Scottish secretary, said he decided with "some reluctance" it was time to move on.
The Labour MP said he wanted to spend more time working towards multilateral disarmament and conflict resolution.
Mr Browne was elected as MP for Kilmarnock and Loudon in 1997. He resigned from the cabinet amid a reshuffle in October 2008.
On announcing his decision to stand down, Mr Browne said: "With some reluctance, I have decided that it is time for me to move on."
'Privilege and honour'
He added it had been an "enormous privilege and honour" to have been an MP, stating: "No-one can have had a better job than I have had for the last 12 years.
"But those who know me best know that it has always been my plan to seek further challenges outside parliament and the time has come for me to put that plan into action."
He added that since his resignation from the government, he had been able to use his experience in working towards multilateral disarmament and conflict resolution.
He said he would not be able to do justice to the full-time job of being MP for his constituency and simultaneously pursue these goals.
He pledged he would continue to be an "active local MP" until the next election and would "vigorously support" the Labour candidate for the seat.