Lord Bourne of Aberystwyth has become the latest addition to the Department of Energy and Climate Change (DECC).
DECC made the announcement on its twitter account.
Lord Bourne has been a member of the Lords since September 2013 and was appointed as a Government Whip (Lord in Waiting) in August last year.
He served as leader of the opposition in the Welsh Assembly from 2007 to 2011.
At the Department for Food, Environment & Rural Affairs (Defra), Liz Truss has retained her role as Environment Secretary, George Eustice is the new Minister and Rory Stewart has become Parliamentary under Secretary of State.