The couple were married in a low-key civil service at the Langar Hall Hotel near Nottingham earlier today, close to where Ms Thornton grew up.
Around 50 family members and friends attended, including his brother David Miliband. The married couple opted not to have a best man’s speech and delivered a bride and groom’s speech instead.
Shortly before the service Mr Miliband took the time to send a tweet to well-wishers:
“Thanks for all the good wishes,” tweeted Mr Miliband. “Really looking forward to the day. Feel like the luckiest guy in the world to be marrying Justine.”
Guests were entertained by a quartet of two trumpets, an oboe and a piano playing classical pieces and heard two readings during the 25-minute service.
One was an extract from Louis de Bernieres’ best-selling novel Captain Corelli’s Mandolin and I Carry Your Heart With Me, a poem by the American writer E.E. Cummings.
Justine will take the Miliband surname but will continue to use Thornton for professional purposes.
After posing for the cameras, the newlyweds went off to join guests enjoying champagne and canapes ahead of the formal wedding lunch.
They will take a five-day honeymoon at a location that hasn’t been disclosed.