Labour leader Ed Miliband said he feels like "the luckiest guy in the world" to be marrying his long-term partner Justine Thornton.
The couple are tying the knot in a low-key civil ceremony attended by around 50 family members and old friends including Mr Miliband's brother David, who he beat for the Labour leadership last year.
The wedding will take place at the Langar Hall Hotel near Nottingham, not far from where Cambridge-educated environmental barrister Ms Thornton grew up.
The groom took time out from preparing to walk up the aisle to send a message on Twitter to followers who had wished him well for the day.
"Thanks for all the good wishes," wrote Mr Miliband. "Really looking forward to the day. Feel like the luckiest guy in the world to be marrying Justine."
The wedding will be followed by a reception at the same venue, including "drinks and canapes" and speeches delivered by the bride and groom only - Mr Miliband having dispensed with the tradition of having a best man.
Mr Miliband, who proposed on London's Primrose Hill near where the couple live with their two young sons, announced in May that they would marry
As the first leader of a major political party to live with his family out of wedlock, Mr Miliband had faced criticism about his unmarried status but insisted he would not be forced into it.
"We'll get married because we want to get married and love each other very much, no other reason," he told one interviewer.
The Labour leader, 41, met Ms Thornton, who is a year younger than him, in 2005 - the same year Mr Miliband was first elected to Parliament.