The court said Choi's crimes were grave given how they led to the impeachment of a president and disappointed the public.
The Seoul Central District Court found Choi guilty of abuse of power, bribery and interfering in government business. She was accused of exploiting her ties with the former president and forcing 50 business conglomerates to pay a combined 77.4 billion won to two nonprofit foundations she controlled.
The court acknowledged that Choi colluded with Park to extort money from the conglomerates including Samsung, Lotte and SK, using presidential connections and abusing power.
For Lotte, a conglomerate with businesses including chemicals and hotels, the decision comes after a sweeping reorganization a year ago that created a holding company for numerous companies assets and consolidated Shin's control.
Reading out the verdict, the judge said Park "abandoned constitutionally-given responsibility and gave position and power to others" and that Choi used her position "to monopolize state business and seek personal gain". Former presidential aide An Chong-bum was sentenced to six years of prison and a fine of 100 million won for corruption.
Shin was immediately put under custody in the courtroom.
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He was arrested in court, having been out on bail during the trial - but smiled calmly after he was sentenced, while his legal team looked grim.
Choi had no title or security clearance, but prosecutors said she interfered in a wide range of official issues, including the nomination of cabinet members and ambassadors - and in editing many of Ms Park's speeches. "We respect the court's decision, but the result is very regrettable". "We will do our best to have a different ruling in the appeals court".
The court ruled that there had been a tacit request from Shin to win duty-free licenses from Park in exchange for W7 billion Lotte paid into Choi's bogus K-Sports Foundation.
The key to the case was whether Samsung Group had sought Park's influence over a state-run insurance corporation in order to exercise its voting right to support a merger of its two affiliates, which was seen as crucial to cementing Lee's control over the country's biggest conglomerate. Choi's sentence is five years shorter than what was demanded by state prosecutors, but it's the heaviest sentence among the people involved in the corruption scandal.
Shin was also fined 7 billion won. Park has refused to appear in court hearings in protest at the decision to extend the presentencing detention of Park for as long as six months in October previous year.
Liberal politician Moon Jae-in was elected the new president in May.