Grenell announced the release via a photo published on X, where he is seen sitting together with the six Americans on board a plane.
According to the White House, the focus of Grenell's trip to Caracas was on President Trump's work to deport Venezuelans from the USA back to their home country.
Maduro was recently sworn in for a third term after an election in July last year, which he is accused by many of having rigged to achieve the alleged victory. He says in a statement after the meeting with Trump's envoy that he wants to see a "new start" in the relationship with the USA.
The Latin American country is under harsh sanctions from Washington.
Last summer, more than 2,400 people were arrested, 28 people were killed and 200 injured in crackdowns on the protests that followed the disputed election.
