Gerard Coyne, who lost the Unite leadership battle to Len McCluskey – has been sacked as the union’s West Midlands regional secretary.
Mr Coyne said he was “deeply disappointed” by his dismissal.
He was suspended in April after accusations of bringing Unite into disrepute.
Mr Coyne said he would appeal against the decision. He said he faced seven charges at a disciplinary hearing.
One charge, he said, related to an alleged technical data breach, which was claimed to have damaged the relationship between Unite and the Labour Party.