Choi Soon-sil (in mask), the jailed confidante of former South Korean president Park Geun-hye, arrives at Seoul Central District Court in Seoul on Tuesday to hear the verdict in her case involving 18 counts of abuse of power, coercion and bribery. Photo: AFP

The secret confidante of ousted South Korean president Park Geun-hye was convicted Tuesday and jailed for 20 years for her key role in the scandal that brought down the head of state.

Choi Soon-sil - who became close to Park through her father, a shadowy religious figure - was vilified during the massive nationwide protests that rocked Asia's fourth-largest economy and culminated in Park's impeachment last year.

The Seoul Central District Court found Choi guilty of abuse of power, bribery and interfering in government business.

The verdict is a potential pointer to the decision in Park's separate trial, since 15 of the 18 charges Choi faced mirror counts on the ex-president's own indictment.

Judge Kim Se-yoon told a packed courtroom that Choi took advantage of "long private ties" with Park to force companies to donate funds to foundations she controlled and used for personal gain.

She accepted more than 14 billion won ($13 million) from telecommunications giant Samsung and retail conglomerate Lotte, he said, and "meddled in state affairs widely."

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 Park's speeches. 

"In light of the size of material gains obtained by the accused, the severe confusion in state affairs caused by her crimes and the people's sense of frustration, the guilt of the accused is very heavy," he said.

She had shown no repentance, the judge added. "The accused is sentenced to 20 years in prison."

Choi, who wore a dark blue coat and a badge bearing her prison number, showed little reaction as the sentence was passed.

Choi's co-accused Shin Dong-bin, chairman of the Lotte group which is South Korea's fifth-biggest conglomerate, was given two and a half years in prison.

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.