66.8% voted 'no' while just 32.2% voted 'yes' - a winning ratio of more than 2:1.
96,000 tenants were balloted and faced widespread campaigning and voting against the transfer by the city council. Almost two-thirds voted.
If endorsed, the stock transfer would have resulted in the privatisation of 2,200 jobs, along with the permanent loss of tenants' rights and the departure of social housing in Birmingham from public ownership and democratic control.
Tracey Twist, Unison branch chair and housing convenor, said:
'We now have a job to do in rebuilding the morale of staff and tenants in Birmingham, and restoring the service to its proper level, as it has been neglected and run-down in an attempt to persuade tenants that stock transfer really was the only option.
'The ballot result shows that the council cannot easily mislead tenants, who are rightly suspicious of the council's behaviour and motives.'
Unison and Defend Council Housing believe the council attempted to massage a 'yes' vote in Birmingham by misleading tenants and leaving out much of the information they would be entitled to in a fair and balanced consultation process.
The council also spent millions of taxpayers' money trying to swing the vote - cash which could have been spent improving the city's housing stock.
Fiona Westwood, regional organiser for Unison, added:
'This is a great day for tenants in Birmingham, who have demonstrated with this ballot result that they are smarter than the council believed.
'Birmingham was the biggest stock transfer ever proposed in Britain, and the government will have to think again about how it finances housing stock investment in the wake of this result.'
And Unison national officer Colin Meech added:
'We are very pleased with the Birmingham result, which is something Unison has campaigned for vigorously. We salute the tenants of Birmingham, who have made a sound judgement based on all the facts, and have not been swayed by the considerable influence of the council's propaganda aimed at persuading them to vote 'yes'.
'Those tenants can rest assured that our campaign for better homes does not end here.'