More than 200 supporters gathered outside the court, holding national flags and signs calling for an end to political revenge against Park. He was sentenced to death but released after two years under a presidential pardon.
The court said Park received bribes worth 7.2 billion won from Samsung Group, though it can not determine how much she kept for herself.
Park, 66, maintains that she's a victim and has been refusing to attend court sessions since October. She cited sickness as the reason for not appearing for the verdict.
The 49-year-old billionaire was found guilty of bribery and other corruption charges last year and sentenced to five years in prison, but in February a higher court reduced his sentence and suspended it for four years.
The former leader previously denied any wrongdoing, and the sentence was announced in her absence.
A South Korean judge said Friday that ex-President Park Geun-hye is guilty of abuse of power and coercion.
Experts said the verdict was as expected and was in line with other verdicts in one of the biggest corruption scandals to have hit South Korea.
The two women were also convicted of taking bribes from some of those companies, including more than 7 billion won (£4.6 million) alone from Samsung in return for government support for a smooth company leadership transition.
But the court said most of Samsung's payments did not constitute bribes.
Park, the daughter of dictator Park Chung-hee, lost both her parents to assassins.More news: Man points gun at officer on bike patrol in south Wichita
Park was accused of being unduly influenced by Choi.
Prosecutors had asked for Park to receive a 30-year sentence. She quickly becomes a heavyweight in conservative politics.
Park was the first female president of the country and is the first president to be impeached. There were no immediate reports of major clashes or injuries.
Park's core supporters have always seen her as a heroically tragic figure who devoted her life to the service of her country despite childhood tragedy.
But the teenage orphan was forgotten about, a legacy of a political era from which South Korea had left behind. But he's also remembered for imprisoning and torturing dissidents.
Park's friendships with Choi, 61, began in the mid-1970s when Choi's late father served as Park's mentor after her mother's assassination.
President Moon Jae-in came to office a year ago on a drive to wipe out what he calls "deep-rooted evil" across society. A presidential election in May saw the victory of liberal Moon Jae-in, whose administration has overseen a thawing of relations between South and North Korea.
She was also convicted of forcing companies to sign lucrative deals with firms owned by Choi and donate gifts to Choi and her daughter.
Much of the public anger was focused on Park's relationship with Choi and accusations that she let her childhood friend - who held no formal position or security clearance - meddle in state affairs, including high-level appointments and editing official speeches.