While almost 80% of the Parliamentary Labour Party formally nominated Mr Burnham last week, extra endorsements on Monday took him over the line.
Andy Burnham will be the next prime minister after receiving an extra 27 nominations from Labour MPs on Monday, taking his total to 349.
The additional nominations, on top of the 322 he received last week, mean it is now impossible for any other candidate to gain the 81 endorsements needed to challenge for the Labour leadership.
While almost 80% of the Parliamentary Labour Party formally nominated Mr Burnham last week, extra endorsements on Monday took him over the line.
As the only candidate to replace Sir Keir Starmer, Mr Burnham is expected to formally take over the Labour leadership at a special party conference on Friday.
He will then become prime minister three days later, on July 20.
Despite being the only candidate, Mr Burnham is expected to take part in an online hustings with Labour MPs later on Monday.
