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.
The extra nominations included backing from Communities Secretary Steve Reed, a key ally of Sir Keir Starmer.
Mr Reed was the only member of the Cabinet not to nominate Mr Burnham last week – Shabana Mahmood and Anna Turley by convention will not nominate anyone because of their positions chairing Labour’s national executive committee and the party respectively.
Sir Keir, as outgoing leader, also by convention does not take part.
Others who nominated Mr Burnham on Monday included junior ministers Sir Chris Bryant and Mike Tapp, former minister Jess Phillips and Richard Burgon, secretary of the left-wing Socialist Campaign Group of Labour MPs.
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.
Labour sources said Mr Burnham would use the hustings to set out his priorities for the country, including devolving power to communities, improving growth across the UK and tackling the cost of living.
He is expected to pay tribute to Sir Keir for delivering on his promise of a Hillsborough Law, which returns to Parliament on Tuesday, and make a pledge to lead from the front on changing the culture within Labour, reiterating his promise to appoint cabinet ministers from across the party.
Mr Burnham is also expected to begin the hustings with a tribute to former Conservative MP Ann Widdecombe who died last week.
Ahead of the hustings, Mr Burnham tweeted that she had been the victim of an “appalling act of violence” and said the police “must be given the resources and space they need so justice can be done as quickly as possible”.
