Olmert, the country's first former premier to serve jail time, did not speak to reporters when leaving the Maasiyahu prison in central Israel.
Wearing a dark-coloured T-shirt, he was seen exiting the jail shortly after dawn on Sunday before being driven away.
The 71-year-old, premier between 2006 and 2009, was convicted of graft and entered prison in February 2016. He had been sentenced to 27 months.
Olmert was granted early release by a parole board on Thursday and prosecutors decided not to appeal the decision.
He had resigned as prime minister in September 2008 after police recommended he be indicted for graft, but remained in office until March 2009, when right-wing Likud leader Benjamin Netanyahu was sworn in to the post, which he has held ever since.
Olmert won international acclaim for relaunching peace efforts with the Palestinians at the Annapolis conference in the United States in 2007, but they failed to bear fruit and the corruption charges against him have come to define his legacy.
The parole board said last week that while Olmert's crimes were "severe," he was "punished for his deeds and paid a heavy price."
"The inmate underwent a significant rehabilitation process in prison and displays motivation to continue it," it said.
"All this significantly diminishes the risk he will deviate again from honest practice."
The decision came after Olmert was recently rushed to hospital after experiencing chest pains in prison.
The former premier underwent examinations which determined he was healthy and he returned to prison after a number of days.
A picture of a gaunt Olmert in hospital robes eating from plastic utensils found its way to social media, evoking a wave of sympathy from the public as well as politicians calling for his early release.
Even after his release, Olmert could still face new criminal charges, though some Israeli media reported that the probe is expected to be dropped.
Last month, the state attorney's office instructed police to investigate suspicions Olmert had smuggled a chapter of a book he was writing out of prison, an act that would constitute a felony due to the "secretive" content, the justice ministry said.
Police had raided the office of the Yediot Aharonot publisher and seized Olmert's manuscript as well as other materials out of fears their dissemination -- prior to the mandatory censorship they would be subject to -- could cause "severe security damage", the ministry said.
The investigation was ongoing, with the state attorney's office expected to announce in the coming days whether it would seek to press charges against Olmert over his conduct around the book.
Olmert's original 27-month prison term was comprised of 18 months for taking bribes in the early 2000s in connection with the construction of Jerusalem's massive Holyland residential complex, eight months for a separate case of fraud and corruption, and another month for obstructing justice.
The main convictions against him dated to before his time as prime minister, to the years when he served as mayor of Jerusalem and economy minister, among other positions.
In a video message released just before he began his sentence, Olmert, a debonair man reputed to have a taste for fine cigars, maintained his innocence.
"You can imagine how painful and strange this change is to me, my family, loved ones and supporters," said Olmert, looking haggard and downcast. "I totally deny all the bribe charges attributed to me."
He added that "over the course of my extensive career I also made mistakes, though none of them were criminal by nature in my opinion. I'm paying a dear price for some of them today, perhaps too dear.
"With a very heavy heart, I'm accepting my sentence today. Nobody is above the law."
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