De facto Deputy Prime Minister Damian Green has resigned following allegations that pornography was found on his Commons computer.
The Ashford MP was asked to step down as First Secretary of State for breaching the ministerial code.
In a letter published on Wednesday night, Theresa May revealed a report cleared him of watching or downloading the porn.
But it found he made two “misleading” and “inaccurate” statements about knowledge of the claims.
Mrs May wrote: “While I can understand the considerable distress caused to you by some of the allegations which have been made in recent weeks, I know that you share my commitment to maintaining the high standards which the public demands of Ministers of the Crown.
“It is therefore with deep regret, and enduring gratitude for the contribution you have made over many years, that I asked you to resign from the Government and have accepted your resignation.”
The letter also said Mr Green, 61, “recognised” he made a female journalist “feel uncomfortable”.
Freelance columnist and daughter of a family friend Kate Maltby, 31, claimed in October she “felt a fleeting hand against my knee” during a meeting in a bar.
In his letter of reply, Mr Green maintained he never viewed or downloaded porn on his Commons computer.
He wrote: “I accept that I should have been clear in my press statements that police lawyers talked to my lawyers in 2008 about the pornography on the computers, and that the police raised it with me in a subsequent phone call in 2013.
“I apologise that my statements were misleading on this point.”
He added he “depply regretted” the “distress” caused to Ms Maltby and acknowledged that he “clearly made her feel uncomfrotable – and for this I apologise”.
Ms Maltby’s parents, Colin and Victoria Maltby, said they were “pleased” the Cabinet Office inquiry had concluded.
“We are not surprised to find that the inquiry found Mr Green to have been untruthful as a minister, nor that they found our daughter to be a plausible witness.
“We have received many supportive messages from people near and far who appreciate Kate’s courage and the importance of speaking out about the abuse of authority.”
His departure marks Mrs May’s third Cabinet resignation in three weeks, after former Defence Secretary Sir Michael Fallon and ex-International Development Secretary Priti Patel stood down.