Members of the Transport and General Workers Union (TGWU) and Amicus have balloted overwhelmingly to form the biggest trade union in the UK.
As yet unnamed, the new union will represent more than two million workers, involved in the transport, manufacturing, farming and aviation industries - among others - as well as the financial and public sectors.
Overall, voters backed merger plans by a margin of more than three to one. Seven in ten members of Amicus supported the move, as did 86 per cent of TGWU members.
Integration will begin on May 1st and is expected to be complete by November next year.
"The new union will be the greatest campaigning force on behalf of ordinary people that has ever existed," said Amicus general secretary Derek Simpson.
"It is a precursor to the creation of a single global trade union movement capable of challenging the might of multi-nationals which seek to play workforces and governments off against each other to reduce jobs and hard-worn pay and conditions."
Mr Simpson and his TGWU counterpart Tony Woodley will jointly lead the new union until 2010.