Gerard Coyne said he would be pressing on with plans to succeed Len McCluskey as general secretary of Unite, after defying the odds to secure the required 172 branch nominations.
The former West Midlands regional secretary of Unite is making his second bid for national leadership of the union having been edged out by Corbynite Mr McCluskey in 2017.
Mr Coyne, from West Bromwich, said: "The confident predictions that I could be kept off the ballot paper have been proven wrong.
“I welcome the opportunity to put my message of change before the whole membership and have it compared to the records of the three continuity candidates.
“Any suggestion that there will be a grubby backroom deal between the three continuity candidates would be both anti-democratic and a betrayal of Unite members' right to choose.
"It would be a betrayal of those members who have already nominated candidates in the belief they were serious about standing.
"It will also show they are running scared and how desperate they are to block real change in Unite.”
The threshold for branch nominations was raised from 50 to 172 after the 2017 leadership election.
Four challengers are vying for leadership, after left-wing candidates Steve Turner, Howard Beckett and Sharon Graham also made the ballot paper.
It has been suggested that two of the left-wing candidates could drop out and rally behind the other one, leaving Mr Coyne with a mountain to climb to secure victory.
In February, Mr Beckett, said: "The right wing will not get on the ballot. It would be a high bar they would have to meet and our branches will not allow that to happen."
He added that if it did happen, "put the lock on the door until the three candidates that describe themselves as of the left reach an agreement as to who the candidate should be".
Mr Beckett, who is Unite's assistant general secretary for politics and legal, was suspended by the Labour Party last month after saying Home Secretary Priti Patel should be deported.
He later apologised but said his suspension was "completely inappropriate".
Mr Coyne has vowed to bring transparency to the union and end its interference in the Labour Party, putting the focus back on members' jobs, pay and conditions.
He was sacked as West Midlands general secretary after the 2017 national leadership campaign, following charges relating to an alleged "technical data breach" that he claimed were "nothing more than a stitch-up".