Tory MP for Braintree Brooks Newmark has resigned as minister for civil society following Sunday Mirror allegations he shared sexually explicit images of himself with an undercover reporter over social media.
He said in a statement he remained "a loyal supporter of this government".
His resignation comes on the eve of the Conservative party conference.
It was announced hours after fellow Tory MP Mark Reckless said he was quitting the party to join UKIP.
It is alleged the reporter was posing as a young female activist.
A Downing Street spokesman said Prime Minister David Cameron had accepted Mr Newmark's resignation as a minister.
Mr Newmark, 56, said: "I have decided to resign as minister for civil society having been notified of a story to be published in a Sunday newspaper.
"I would like to appeal for the privacy of my family to be respected at this time.
"I remain a loyal supporter of this Government as its long term economic plan continues to deliver for the British people."
Mr Newmark, who has been the MP for Braintree since 2005, became minister for civil society in July.
No 10 said later that Rob Wilson, Conservative MP for Reading East, had been appointed as Mr Newmark's replacement as minister for civil society.
Mark Reckless earlier told the UKIP conference he had resigned as an MP, triggering a by-election in Rochester and Strood.
He will seek re-election in his constituency for UKIP.