Nadia Akacha had been a key aide to Saied until she quit in January last year, citing "fundamental differences of opinion" over the national interest.
On Tuesday, a Tunis court sentenced Akacha in absentia to 14 months in jail, local media reported, adding that the sentence was in relation to a suit filed by the president's sister-in-law.
11 audio recordings appeared online featuring a woman, purportedly Akacha, relating details from private meetings since the president's July 2021 power grab.
In some, the woman criticised the president and staff members or shared gossip about his in-laws.
Akacha has denied being the woman in the recordings, describing them as fakes aiming to undermine her former boss.
Prosecutors had opened an investigation in May to determine the recordings' authenticity.
Akacha left the country after her resignation. Tunisian media have reported she has since been living in France.
A constitutional lawyer like the president, she was appointed as Saied's legal adviser in late 2019 before becoming his chief of staff in January 2020, travelling widely with him domestically and abroad.
Her departure was a blow to Saied six months after he suspended parliament and sacked the government in a shock move against the political system that had emerged from the country's 2011 revolt.
Many Tunisians initially welcomed his moves but others have accused him of seeking to reinstall an autocracy in the birthplace of the Arab Spring uprisings.