Henrietta Rushwaya, president of the Zimbabwe Miner’s Federation, was caught with 6kg of bars in 2020.
She was travelling from Harare to Dubai when the contents of her handbag were picked up by the airport scanner.
Ms Rushwaya said she had picked up the wrong bag, but was charged with having an invalid export licence.
All gold exports must be accompanied by a licence.
Ms Rushwaya is not related to the President of Zimbabwe by blood, but in the traditions of her Shona ethnic group she is considered to be his niece.
She was remanded in custody and awaits sentencing on 10 November.
Ms Rushwaya was charged alongside two agents of the country’s national intelligence agency, who were both acquitted for lack of evidence.
Her conviction followed an undercover investigation by Al Jazeera journalists.
They alleged that huge amounts of gold were being smuggled from Zimbabwe to the United Arab Emirates by people with links to senior government officials.
They said networks of dormant companies, fake invoices and bribed officials had been used.
Following the documentary, the government announced it was launching an investigation.
“Any person found to have been involved in acts of corruption, fraud or any form of crime will face the full wrath of the law,” it said.
President Mnangagwa, who came to power in 2017 after the military staged a coup against long-time leader Robert Mugabe, has vowed to tackle corruption.
He was re-elected for a second term a few months ago with 52.6% of the vote in an election the opposition said was marred by widespread fraud.
His critics say little has changed since he became president.
