Len McCluskey has been elected the next general secretary of Unite, the country's largest trade union.
Just over 15% of the 1.57-million membership voted in the four-way leadership race, which was seen as a battle between McCluskey and Bayliss, his fellow assistant general secretary.
Unite members opted for McCluskey, a former dock worker and centre-left candidate, over Bayliss. Bayliss raised eyebrows on the eve of the TUC conference – at which unions vowed to mount a mass campaign of action to defend public services from government cuts – by declaring that public sector strikes would turn unions into the "bad guys".
McCluskey's victory heralds a leftwing leadership that will be at the forefront of moves to oppose government cuts.
He secured around 101,000 votes, with Jerry Hicks, a popular grassroots leftwing activist, coming in second on 52,000 votes. Bayliss was pushed into third place on 46,000 votes while Gail Cartmail, assistant general secretary with responsibility for public services, came fourth, with 39,000 votes.
Derek Simpson, formerly of Amicus, retires as joint leader next month. Tony Woodley, formerly of the T&G, will step down next autumn.