With the nation transfixed and Israeli television broadcasting live, the 70-year-old entered the Maasiyahu prison in the central city of Ramle just before 10:00 am (0800 GMT).
He was escorted to the prison by officers of Israel`s Shin Bet domestic security agency as a crowd of journalists watched from nearby.
A debonair man reputed to have a taste for fine cigars, Olmert`s prison term closes a chapter in a long legal odyssey since he left office in 2009.
The charges against him date 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 on Monday morning before he began his sentence, Olmert 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."
Four pair of underpants
Olmert was initially given six years` prison in May 2014 for taking bribes in the early 2000s in connection with the construction of Jerusalem`s massive Holyland residential complex, but the sentence was later reduced to 18 months.
Last week, an Israeli court handed him an additional month for obstructing justice. He admitted to the crime as part of a plea bargain in that case.
His prison sentence could still be extended further. The Supreme Court is debating his appeal against a third sentence of eight months for fraud and corruption.
The former leader of Israel`s opposition Labour party, Shelly Yachimovich, said there were some positives to draw from Olmert`s jailing.
"The saddening fact that a convicted prime minister is entering prison this morning is testimony to the resilience of our democracy, the equality before the law and the elimination of corruption," she said on Twitter.
The Israeli Prisons Service says Olmert has been assigned to special block 10, "which is intended to house prisoners who for various reasons cannot be placed with the general prison population."
He will join four other unidentified inmates in block 10, which has a maximum capacity of 18, and he will eventually have to share a cell.
Inmates are allowed to bring from home four pairs of underpants, four pairs of socks, two towels and two sweatshirts without hoods or lining.
They can also bring with them one blanket (not a duvet), two sheets, a pillowcase, and religious books and articles.
Luxury travel and cigars
Born near the port city of Haifa, Olmert was elected to parliament in 1973 for the rightwing Likud party and served as mayor of Jerusalem from 1993 to 2003. He later joined the cabinet.
He broke away from the Likud with then-prime minister Ariel Sharon in 2005 to form the centre-right Kadima party and became premier the following year after Sharon suffered a massive stroke and slipped into a coma.
Olmert resigned as prime minister in September 2008 after police recommended he be indicted for graft, but he remained in office until March 2009, when 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 the corruption charges against him have come to define his legacy.
US financier Morris Talansky, a key witness in one of the cases, testified that Olmert gave him envelopes stuffed with cash and said much of the money may have been spent on luxury travel and fine cigars.
The testimony sent shock waves through Israeli politics.
Before taking over as premier in 2006, Olmert was recognised as a key strategist behind many of Sharon`s boldest moves, including Israel`s 2005 withdrawal from Gaza and his decision to leave Likud and form Kadima.
He was once seen as among the most promising politicians in Israeli history.
Israel ex-PM Olmert begins prison term for corruption
16 February 2016
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Ehud Olmert, once feted for his peace efforts with the Palestinians, on Monday became Israel`s first former premier to serve jail time as he began a 19-month sentence for bribery and obstruction of justice.
