Lord Marland stands down as business minister
Lord Marland has become the second Tory minister in the House of Lords to stand down in a matter of days.
No 10 said the business minister had resigned from his position to "focus on his role in trade promotion".
A former Conservative Party treasurer, Lord Marland became a peer in 2006 and has held a number of jobs, first in opposition and then in the coalition.
His decision follows that of Lord Strathclyde to quit as Lords leader after 14 years on the Tory front bench.
Both men have signalled their intention to focus on outside business interests.
Since September Lord Marland has been an unpaid junior minister in the Department for Business, Innovation and Skills - acting as the government's business spokesman in the House of Lords - having previously held a similar role in the Department for Energy and Climate Change.
Before accepting a peerage, he was a senior insurance executive.
Energy minister Greg Barker tweeted that he was "very sorry" to see Lord Marland leave the government, saying he had done a "fantastic job" and ministers had benefited from his "business brain".
But Labour said his departure, following that of Lord Strathclyde on Monday, showed the government was in "total chaos".
"Just one day after their botched relaunch, even people at the very heart of Cameron's government are losing faith and abandoning ship," said shadow cabinet office minister Michael Dugher.
The BBC's political correspondent Vicki Young said Lord Marland was "quite a close friend" of Lord Strathclyde so the timing of his departure was unlikely to be much of a coincidence.
Lord Marland was the only business minister in the Upper House, she added, and his departure reflected both his frustration at the job he was having to do there and his belief that he could achieve more as the prime minister's trade envoy.