Sean Turnell, an associate professor in economics at Sydney’s Macquarie University, who had served as an adviser to Ms Suu Kyi, has been sentenced after being tried and convicted under the secrets law, an official said to The Associated Press.
The trial was conducted in a purpose-built courtroom in Naypyitaw’s main prison and was closed to the media and the public.
A gag order also barred the defense lawyers from revealing details of the trial proceedings.
Three members of Ms Suu Kyi’s cabinet were also found guilty, each receiving sentences of three years.
In February last year, Ms Suu Kyi was detained in the capital Naypyitaw when her elected government was ousted by the army.
Mr Turnell was charged with Ms Suu Kyi and her three former cabinet ministers on the basis of documents seized from them.
However, the exact details of their offence has not been made public.
Last year Myanmar’s state television said that Mr Turnell had tried to flee the country and had access to “secret state financial information”.
It is also not clear what sentence he has received for the additional charge he faced for violating immigration law.
Under Myanmar’s Official Secrets Act, the possession, collection, recording, publishing, or sharing of state information that is “directly or indirectly, useful to an enemy” is a criminal offence. The charge carries a maximum penalty of 14 years in jail.
Mr Turnell’s sentencing has been condemned by Australia, which has demanded his release.
Foreign minister Penny Wong said on Thursday: “The Australian government has consistently rejected the charges against Professor Turnell during the more than 19 months he had been unjustly detained by the Myanmar military regime.”
She added that Australia will continue to advocate for his release and return to Australia.
Since her detention last February, Ms Suu Kyi has already been sentenced to 20 years’ imprisonment after being convicted of illegally importing and possessing walkie-talkies, violating coronavirus restrictions, sedition, election fraud, and five corruption charges.
She is also being tried on seven counts under the country’s anti-corruption law, with each count punishable by up to 15 years in prison and a fine.
The cases against the former leader are widely seen as being concocted to deter her from returning to active politics.
(Additional reporting by agencies)