Prosecutors had sought a 30-year sentence.
Park was once again absent for Friday's hearing.
Park was the first female president of the country and is the first president to be impeached.
Outside the court, hundreds of supporters of Park had gathered to watch the verdict on a large screen, waving Korean and United States flags and calling for the former president's release.
Amid all the political point scoring and legal procedures, massive protests triggered across South Korea both in support and against Park.
South Korean ousted leader Park Geun-hye arrives at a court in Seoul, South Korea, August 25, 2017. That feeling has only grown with the arrest of Park's predecessor on unrelated corruption charges.
But in 2016, reports of Choi's influence emerged, leading to revelations that she had been extracting money from big businesses on the president's behalf. She says she is a victim of politics.
2012: Park wins the presidency by defeating her main liberal rival, Moon Jae-in.
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. She has previously maintained her innocence. Ten days later, she is arrested.
President Moon Jae-in came to office a year ago on a drive to wipe out what he calls "deep-rooted evil" across society.
Apparently this was as a result of a scandal that exposed webs of corruption between political leaders and the country bigwigs.