Choi was at the heart of a massive corruption scandal that brought down Ms Park, the country's first female president.
She had acted for years as an adviser to Ms Park, who has been impeached and is also on trial.
Ms Park has denied any wrongdoing.
The Seoul Central District Court also fined Choi 18bn Korean won ($16.6m; £12m).
Choi was accused of using her presidential connections to pressure conglomerates - including electronics giant Samsung and retail group Lotte - for millions of dollars in donations to two non-profit foundations she controlled.
"The guilt of the accused is heavy," the judge said, adding that she had capitalised on her "long private ties" with Ms Park to solicit bribes and had "meddled in state affairs widely".
Choi is already serving a three year jail term for a separate charge of corruption, after she was found guilty of using her position to solicit favours for her daughter.
Ms Park meanwhile has been accused of colluding with Choi. She is currently in custody, with a verdict expected later this year.
The court has also found Shin Dong-bin, chairman of the Lotte Group, guilty of offering bribes to Choi, and jailed him for two years and six months.
Ms Park was officially ousted in March 2017, following parliament's decision to impeach her. She was the country's first democratically-elected president to be forced from office.
After losing her presidential immunity, she was charged with bribery, abusing state power and leaking state secrets, and her trial began in May.
When the allegations first emerged they prompted numerous mass protests in South Korea, many of which called for Ms Park to step down.
The controversy has fuelled discontent against the government, the political elite and family-run conglomerates which dominate South Korea's economy.
More about: SouthKorea
