Adrian Nastase, the most senior politician to be jailed in Romania since 1989, when communism collapsed, went free after judges voted to allow his immediate release from Jilava prison, where he was serving a two-year sentence.
His attorney had requested his release due to the fact he is over 60, had written books and had taught fellow prisoners in jail.
Nastase said he looked forward to "breathing freedom" and maintained his innocence. He left the prison, 20 kilometers (11 miles) south of the capital, in a limousine accompanied by his elder son Andrei.
"I am very happy for him and his family and I am waiting to see him," said Prime Minister Victor Ponta, adding that his former mentor would be welcomed back into the Social Democracy Party that he led until 2005.
Nastase, 62, was sentenced in June for illegally raising money for a failed presidential campaign in 2004. He shot himself after learning he would be incarcerated. He served as prime minister from 2000 to 2004.