Basuki Tjahaja Purnama, known as Ahok, was the first ethnic Chinese Christian to run Indonesia's capital, and the case was seen as a test of the country's religious tolerance.
He was accused of insulting Islam by referring to a verse in the Koran during a campaign speech.
He denied blasphemy, but it sparked outrage among religious hardliners.
They staged regular large rallies calling for him to face trial, with some extremists even calling for him to be executed.
Riot police outside court
Ahead of the verdict, protesters for and against Mr Purnama had gathered outside the Supreme Court in Jakarta demanding respectively his acquittal or a long prison sentence.
Around 15,000 security personnel from the police and military are providing security at the scene, with riot police and armoured vehicles separating the groups.
Those against the governor demand a long prison sentence
Mr Purnama became Jakarta's first non-Muslim governor for 50 years when he took over from Joko "Jokowi" Widodo, who was elected president in 2014.
It was significant because as an ethnic Chinese Indonesian and a Christian he is a double minority in Muslim-majority Indonesia.
His political success was also seen as a significant development given the violent anti-Chinese riots that occurred in the city in 1998.
Before the blasphemy allegations, he had been widely hailed as a straight-talking politician with a strong anti-corruption stance
But the controversy overshadowed scheduled elections last month.
Despite his enduring popularity with many in Jakarta for his efforts to improve living standards, he lost to conservative Muslim candidate Anies Rasyid Baswedan.
Indonesia is the world's most-populous Muslim country. About 85% of its population are Muslim, but the country officially respects six religions.