The Transport and General Workers Union (T&G) and Amicus have voted to form the country's biggest union.
Derek Simpson and Tony Woodley will lead the union until 2010
Eighty-six per cent of T&G voters backed the merger, while 70% of Amicus voters were in favour, although the turnout was only just over 27%.
"When we stand together our opponents, bad bosses and callous governments suddenly start to look much smaller," the heads of the two unions said.
The 2m members account for about one-third of all UK union members.
Amicus General Secretary Derek Simpson does not intend to stop with the creation of the super-union.
"It is a precursor to the creation of a single global trade union movement capable of challenging the might of multinationals," he said.
Mr Simpson and T&G boss Tony Woodley will be joint leaders of the new union until 2010.
The new union, which has not yet been named, will officially come into being on 1 May.