Former UK PM David Cameron has stood down as an MP, triggering a by-election in his Oxfordshire seat of Witney.
Mr Cameron, 49, who resigned as prime minister after June's EU referendum, said he did not want to be a "distraction" for new PM Theresa May
He said Mrs May had "got off to a cracking start", while she praised his "great strides" on social reform.
Mr Cameron, 49, has represented Witney since 2001, becoming Conservative leader in 2005 and PM in 2010.
Speaking in his constituency, he said it had been a "great honour" to be an MP for the area, but said it would be difficult for him to remain on the backbenches without becoming "a big distraction and a big diversion" from the work of the new government.
He denied his announcement was related to the government's moves towards allowing new grammar schools, a policy he rejected as PM.
He said the timing was coincidental, adding that there were "many good things" in the proposed education reforms.
"Obviously I'm going to have my own views about different issues," he said.
"People would know that and that's really the point. As a former prime minister it is very difficult, I think, to sit as a backbencher and not be an enormous diversion and distraction from what the government is doing."