Mr Goulart's remains were exhumed in November last year from a cemetery in his home town, Sao Borja, and taken abroad for testing.
The results of the tests were announced in Brasilia by Human Rights Minister Ideli Salvatti.
She described the investigation as a victory for democracy.
"A dictatorship can order an assassination for political reasons, but only a democracy can investigate the reason for a political assassination," said Ms Salvatti.
Despite the announcement, Brazil's National Truth Commission, which started work in 2012, said it would carry on investigating the circumstances around Mr Goulart's death.
Around that time
Condor