The Seoul Central District Court found her guilty on 16 out of 18 charges.
The former President was found to have colluded with her close friend, Choi Soon-sil, to pressure conglomerates for bribes in return for political favours. Choi had no official title and no security clearance, but saw Park much more frequently than the president's own staff.
"The accused abused the power bestowed by the people - the true ruler of this country - to cause chaos in national administration", said Judge Kim Se-yoon, delivering the ruling.
She was dismissed in March 2017 after being impeached but denied wrongdoing, Channel News Asia reports. She is the first South Korean president to be removed from office through a court proceeding and the third president to be convicted of a crime.
The protests show how deeply South Koreans are split along ideological and generational lines, the result of decades-long tension with rival North Korea and the lingering fallout from the conservative military dictatorships that ran the country until the late 1980s. She was indicted the following month. She has one week to appeal the verdict. "She has to take heavy responsibility to make sure a president of the country does not abuse his or her power again".
The scandal has already led to the arrests, indictments and convictions of dozens of high-profile government officials and business leaders.
Moon's office described Park's fate as "heartbreaking" for the nation.
The daughter of dictator Park Chung-hee - assassinated in 1979 - Park held office from 2013 until March 2017, when she was stripped of her powers after the country's Constitutional Court upheld a parliamentary vote to impeach her.
The former president, South Korea's first female leader, was also fined 18bn won (£12m).
She was also convicted of collecting or demanding a total of almost $22 million in bribes from three of South Korea's top business conglomerates, including Samsung, Lotte and SK.
"Given her attitude and public anger over her scandal that remains raw, it will be hard to create a political environment in favour of her release any time soon", Jeong told AFP.
Younger, liberal voters, who staged months of protests against Park before her ouster, will be hoping the verdict will mark a major step towards ending the self-serving collusion between political leaders and the chaebol conglomerates.
She was arrested shortly afterwards, and has been in detention ever since.
Chun's successor, Roh Tae-woo, was also convicted of treason, mutiny and corruption in 1996 and jailed for more than 22 years but served just over two years before being released.
2006: Park, the leader of the main conservative opposition party, is attacked by a man wielding a box cutter while she was campaigning for upcoming elections.