Peter Sunde's lawyer Peter Althin confirmed his client's release to news agency AFP. He served two-thirds of an eight month sentence which began after an appeal in 2010.
"My body just got reunited with my soul and mind, the parts of me that matter and that never can be held hostage," Peter Sunde wrote on Twitter, according to AFP.
Sunde, 36, had been living under a false identity in southern Sweden when police finally caught up with him in May after a two-year hunt.
He and the site's other founders Fredrik Neij and Gottfrid Svartholm Warg had been sentenced on appeal to various prison terms and order to pay a fine of SEK 46 million for copyright infringement. Site financier Carl Lundström was also sentenced to four months in prison.
Neij, the last original founder of the site at large, was arrested last Monday on Thailand's border with Laos. His capture came just days after Warg was sentenced by a Danish court to three years and six months in jail for "hacking and aggravated vandalism" in the largest such case in the country's history.
Founded in 2003, The Pirate Bay allows users to avoid copyright fees and share music, film and other files using bit torrent technology, or peer-to-peer links offered on the site.