Just over a quarter (26 per cent) of the Community and Youth Workers' Union's 5,000-strong membership took part in the ballot, with 82 per cent voting in favour of the merger, which was first mooted in early 2005.
Union general secretary Doug Nicholls said the merger would place the organisation in a strong position to expand membership and advance the status of informal education staff.
"The first thing this does is bring in 350 more full-time officers throughout the UK and Ireland, to help unionise and protect youth, community and play workers," he said. "It helps bring the cause of the youth service and youth work much more naturally into the trade union and political agenda."
Transport and General Workers' Union general secretary Tony Woodley said the decision was an opportunity to boost his union's membership in the voluntary sector.
The merger will come into effect in November. It will not result in changes to subscription levels until discussions have taken place with members.
