The trade minister's departure came after the Coalition Government's Leader in the Lords, Lord Strathclyde, announced on Monday he would quit and will be seen as a damaging blow to the Tory-LibDem Coalition Government.
Lord Marland, 56, is a close friend of the Prime Minister and is thought to have told him yesterday, the day after Lord Strathclyde had left to concentrate on his outside business interests.
The latest loss emerged just 24 hours after a much-hyped relaunch press conference at Downing Street with Mr Cameron and deputy Prime Minister Nick Clegg.
But their resignations will be seen as a sign of continuing difficulties within the Conservative end of the Coalition Government, which spent much of last year fighting battles with the rebels on its backbenches.
Lord Marland, a multimillionaire venture capitalist, is a former Conservative Party treasurer who in his business career led a consortium that rescued Hunter Wellington Boots from administration.
He was made a life peer in 2006 and served as an opposition whip and spokesman in the Lords.
He was treasurer for Boris Johnson's successful mayoral campaign in 2008 and made an unsuccessful bid for chairman of the England and Wales Cricket Board in 2009.
He first joined the Coalition as an energy minister and moved to his new role in last year's reshuffle.
He was brought into the Coalition in part because of his business record as Mr Cameron tried to boost the UK's faltering economy.
During his time in Government he also served as chairman of the British Business Ambassadors group at UK Trade & Investment (UKTI).
He was appointed to a junior ministerial job in the Department of Energy and Climate Change after the formation of the Coalition Government in 2010 and moved to the Department for Business in last year's reshuffle.
He travelled the world representing Britain as Mr Cameron's trade envoy. This has included trips to Saudi Arabia, Kuwait, South Africa, Burma, Thailand and Hong Kong.
However, Lord Marland caused controversy by joking to peers that he would actually spend his time 'bathing in sunshine' on a trip to Mozambique in October last year.
He has also been heavily involved in the UK's attempts to win major contracts around the world following the London Olympics.
Lord Marland told peers that, following a trip to Rio, he was "catching a plane to sub-Saharan Africa' before adding: "'I am just trying to keep the sun tan up."
A Downing Street spokesman said: "Lord Marland will be stepping down as a Minister in order to focus on his role in trade promotion."