The decision by the shopworkers’ union represents a major blow to the campaign of Jess Phillips, as it was the only one of the “big five” unions thought to be considering offering her its endorsement.
Ms Phillips and fellow contender Emily Thornberry now face the tough challenge of winning the nominations of 33 constituency Labour parties if they are to claim a place in the final line-up for a members’ vote which will decide the new leader on 4 April.
Usdaw also nominated runaway favourite Angela Rayner for deputy leader.
The union’s general secretary Paddy Lillis said: “Usdaw believes that Keir Starmer and Angela Rayner are the right leadership team to unite and rebuild Labour after a devastating election loss. Our members desperately need Labour in power, they cannot afford another decade of Conservative governments attacking workers’ rights, incomes and public services.”
In an apparent signal that the union saw Ms Phillips and left-wing favourite Rebecca Long-Bailey as insufficiently experienced to run the party, Mr Lillis added: “The Labour Party must be led by someone who can persuade voters that they have what it takes to be a prime minister and we are a government in waiting.
“That is at the heart of Usdaw’s decision to make these nominations.”
Having already won the endorsement of Unison and the Socialist Environment and Resources Association (Sera), Starmer has now cleared the hurdle of three affiliated organisations representing at least 5 per cent of affiliated members.
He said: “I’m honoured to have received Usdaw’s endorsement for the Labour leadership. Our campaign is building unity across the labour movement, amongst trade unionists and members.
“Usdaw represent over 400,000 workers and fights every day for its members and for a fairer society.
“If I’m elected leader, Labour will stand shoulder to shoulder with the trade union movement as we take on the Tories and rebuild trust with working people.”
Wigan MP Lisa Nandy has already bagged the support of the National Union of Mineworkers, and is thought likely to secure her place on the ballot paper by winning the nomination of the GMB, which will make its decision on Tuesday following a hustings before its executive committee.
Ms Long-Bailey will have to wait to hear whether her hopes are fulfilled of nominations from the left-leaning Unite and CWU unions.
Unite general secretary Len McCluskey has warned that the decision has not been made and will be decided by the union’s executive council on 24 January. And the CWU’s final decision will be made by 500 delegates at a special conference at the end of this month.