Len McCluskey has won the backing of most of the Unite union's officers, regions and executive members in his bid to be re-elected general secretary.
Nine out of Unite's 10 regions as well as the vast majority of officers, sectoral and regional committee chairmen and members of the union's executive support him.
The election will be held in March and April, with Mr McCluskey being challenged by regional official Gerard Coyne.
Mr McCluskey said: "I am deeply honoured to have received the overwhelming support of the people who give their time to build this great union and defend our members.
"Their vote of confidence in me is phenomenal."