El-Heni emerged from court on Thursday morning to say the deputy public prosecutor had decided to let him go, but that investigations against him would continue.
"If they think they can silence me, they're wrong," he told journalists.
El-Heni, 59, was kept in custody after being questioned on Tuesday evening over alleged "crimes through telecommunications" channels, his lawyer said at the time.
The interrogation took place after el-Heni had mocked an article of the penal code related to "criticizing the head of state," currently President Kais Saied, during a morning broadcast on IFM radio station.
The SNJT journalists' union had called El Heni's arrest a "flagrant violation of the law".
In May, journalists staged a protest to denounce the Tunisian government's "repressive" policy, which they say uses the judicial system to intimidate and subjugate the media.
Around 20 journalists are being prosecuted for their work in the country, according to the union.
Non-governmental organizations have reported a decline in press freedom in Tunisia since Saied launched a power grab in July 2021.