Mr Fallon has been criticised for repeatedly touching journalist Julia Hartley-Brewer's knee during dinner.
British Defense Secretary Michael Fallon has resigned from office following accusations he inappropriately touched a journalist's knee.
The Defence Ministry confirmed he had stepped down.
The MP, who represents Sevenoaks to London's southeast, wrote in a letter to UK Prime Minister Theresa May: 'A number of allegations have surfaced about MPs in recent days, including some about my previous conduct.
After sexual abuse allegations against Hollywood film producer Harvey Weinstein prompted hundreds of thousands of women and men to share stories about inappropriate behavior, Britain's parliament - a bastion of tradition - has been no exception.
He added that it had been a "privilege" to have been defence secretary over the past three-and-a-half years.
As Fallon appeared on television to read a prepared statement, repeating his letter to May, the U.S. government said the resignation "should in no way impact our relationship" with Britain.
According to BBC, May also appreciated the "particular example you [Fallon] wish to set servicemen and women and others".
On behalf of all those you have helped throughout your time in Government, I thank you for your service.
The British prime minister has ordered an investigation into the allegations against Conservative members, including Cabinet minister Damian Green.