Her conviction for soliciting favors for her daughter is the first in a wide-reaching influence-peddling scandal which brought down President Park Geun-hye.
Choi Soon-sil had acted for years as an adviser to President Park Geun-hye, who has been impeached and is also on trial.
She also faces charges that she accepted bribes for Park Geun-hye.
Park Geun-hye has denied all allegations of corruption.
Choi Soon-sil was found guilty of using her position to influence officials at a university to admit her daughter, Chung Yoo-ra, as well as give her daughter grades for papers or exams she never took.
According to the Yonhap news agency, the court stated in its verdict that “she committed too much wrongdoing to consider the actions were out of love as a mother who wants the best for her child”.
Two former officials at the prestigious Ewha Womans University in Seoul have also been jailed for colluding with Choi Soon-sil.
Choi Soon-sil still faces other charges including abuse of authority, coercion, attempted coercion and attempted fraud.
Prosecutors say Chung Yoo-ra, a 21-year-old award-winning dressage rider, was involved in economic crimes, exam fraud, obstructing business and concealing criminal proceeds.
She has denied all these accusations and said she had no knowledge of her mother’s dealings, including those with Park Geun-hye.
Chung Yoo-ra was arrested in Denmark earlier this year and extradited to South Korea.
She is currently not in detention in Seoul. On June 20, a local court said there was no need to detain her and refused the prosecution’s request for an arrest warrant.
Choi Soon-sil is on trial accused of using her presidential connections to pressure companies to give millions of dollars in donations to two non-profit foundations she controlled.
In exchange, it is alleged they received preferential treatment from the government.
Park Geun-hye is alleged to have been personally involved, instructing Choi Soon-sil and two presidential aides to collect money for the launch of the foundations.
The claims have swept up some of South Korea’s biggest companies, including electronics giant Samsung.
Samsung VP Lee Jae-yong is on trial. Several other Samsung executives and former presidential aides are also either facing trial or are under investigation.
Choi Soon-sil is also accused of having received confidential government documents from Park Geun-hye.
Park Geun-hye was arrested in April and preliminary hearings began in May.
The former leader has previously admitted to some lapses, such as consulting Choi Soon-sil for advice and letting her edit presidential speeches, and has apologized for them.
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