The Seoul Central District Court ruled Park guilty of bribery, extortion, abuse of power and other charges. The court's chief judge said the punishment was necessary to prevent similar wrongdoing by other presidents in te future.
Along with the prison sentence, Park was fined more than $16 million. The former South Korean leader has one week to appeal the ruling. Park has continued to say she is innocent of any wrongdoing. She says she is a victim of politics.
Government lawyers had demanded a 30-year prison term.
Park was accused of working with her longtime friend Choi Soon-sil to force businesses to give $72 million to start two foundations. Choi controlled both organizations. The two women were also found guilty of taking bribes from some of those companies.
Park was removed from office early last year following months of protests. Millions marched calling for her ouster.
She is a daughter of leader Park Chung-hee, who ruled South Korea for about 18 years until his death in 1979.
I'm Kelly Jean Kelly.