The Livingston MP Jim Devine is to step down from his government post in protest over plans to replace the Trident nuclear weapons system.
Mr Devine took over from Robin Cook as Livinston MP
Mr Devine confirmed he will resign as a ministerial aide next week over the Clyde-based missile carrying submarines.
A Commons vote is to be held on Wednesday on replacing the Trident system with a new nuclear system.
Mr Devine said he intends to vote against the government's plans.
The vote will determine whether a new generation of nuclear submarines are aquired and the Trident D5 missiles updated.
Last December, Tony Blair said that Britain must keep such an independent nuclear deterrent - at a cost of up to £20bn over 30 years.
Mr Devine won his Livingston seat following the death of Robin Cook, for whom he had been election agent.
Since last October, he has been a parliamentary private secretary to Health Minister Rosie Winterton.