Former prime minister Ehud Olmert was granted early release Thursday from a 27-month prison sentence for corruption scandals that rocked Israeli politics and made him the first ex-premier to serve jail time.

A six-person parole board overruled the state attorney office's objections and "ordered the early release of the prisoner," its decision said.

His release, scheduled for Sunday, would be after he completes two-thirds of his sentence. Prosecutors can however appeal the decision.

While Olmert's crimes were "severe," he was "punished for his deeds and paid a heavy price," the parole board said.

"The inmate underwent a significant rehabilitation process in prison and displays motivation to continue it," it added.

"All this significantly diminishes the risk he will deviate again from honest practice."

Olmert's lawyer Shani Illouz said the former prime minister was "happy" but still concerned about fresh allegations against him involving a book he is writing.

"The committee accepted all our arguments," Illouz told public radio after the decision was read out in the Maasiyahu prison in central Israel.

"As of now, Olmert will be released on Sunday."

Olmert is Israel's first former premier to serve jail time.

He 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 committee's decision comes after Olmert was rushed to hospital after experiencing chest pains in prison last week.

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.

'Impeccable' prison behaviour

Even with his impending release, Olmert could still face new criminal charges.

Earlier this 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 justice ministry said.

The investigation was ongoing, with the state attorney’s office expected to announce in the coming days whether they would seek to press fresh charges against Olmert over his conduct around the book.

The parole board had in its Thursday decision addressed the issue, rejecting the state attorney's argument that it displayed "a pattern of ongoing dishonesty" and maintaining instead that it was a "disciplinary offence" that did not reflect Olmert's largely "impeccable" behaviour.

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."