Len McCluskey has been re-elected as general secretary of Unite after beating his nearest rival by over 5,500 votes.
Mr McCluskey polled 59,067 votes against 53,544 for Gerard Coyne and 17,143 for Ian Allinson.
The turnout was 12.2%.
Unite's acting general secretary Gail Cartmail said: "I congratulate Len McCluskey on his victory and would urge the entire union to pull together in the interests of our members, and not least to work for a Labour victory in the general election.
"The turnout in this important election can give no cause for satisfaction and, while the tone of the campaign will not have helped, the underlying reason remains the archaic and expensive balloting system imposed on trade unions by law.
"The sooner we can more to secure and secret workplace and online voting the better for union democracy."
Mr Coyne was surprisingly suspended from his post as the union's West Midlands Regional Secretary on Thursday.
An email was sent to Unite members and staff in the West Midlands informing them that Mr Coyne had been suspended from his job pending an investigation into "certain issues."