He was mayor of Jerusalem from 1993 to 2003, and took over as prime minister in 2006 after a stroke incapacitated Ariel Sharon.
Two years later, he resigned amid a corruption scandal, and was charged and imprisoned last year.
Israeli Prison Service spokesman Assaf Librati confirmed his release.
American businessman Morris Talansky told prosecutors that he donated or loaned thousands of dollars to Olmert for political reasons, but he appeared to pay for luxury expenses instead.
“I only know that he loved expensive cigars. I know he loved pens, watches. I found it strange,” Talansky testified in 2009. He said he gave Olmert $150,000 in loans and direct payments over 14 or 15 years.
During the trial in 2015, the businessman described how he would go to hotels and hand over envelopes stuffed with cash to Olmert.
He said he once paid for Olmert’s $4,700 hotel bill at the Ritz-Carlton in Washington.
In another instance, the businessman gave him a $15,000 loan and asked him to return the money as soon as possible.
“Famous last words,” Talansky said, explaining that he hadn’t been repaid.