Ms Park, who was very popular when she came to power in 2012, was impeached and removed from office in March following mass protests.
Once impeached, she lost presidential immunity and is facing charges including bribery, abusing state power and leaking state secrets.
Ms Park has always denied wrongdoing.
She has been in detention since shortly after her impeachment and has insisted that she is being framed.
Her removal from office triggered an election that took place earlier this month. It was won by her 2012 election rival, Moon Jae-in.
The trial in Seoul, which Ms Park is obliged to attend, is expected to last several months and will draw in some of South Korea's biggest companies and political names.
The maximum sentence for corruption in South Korea is life.
What is Ms Park accused of?
She is facing a total of 18 charges including bribery, abuse of power, coercion and the leaking of government secrets.
The charge sheet runs to about 120,000 pages, South Korean media report, and mostly relates to the alleged activities of her close friend, Choi Soon-sil.
Ms Choi is accused of using her connections with the president to pressure some of the country's biggest companies to give money to a foundation she established in exchange for favourable treatment from the government.
Prosecutors say Ms Park colluded with her friend and that between them they secured tens of millions of dollars for themselves.
Ms Park is also accused of leaking state secrets by giving Ms Choi access to her work - including asking her to edit her speeches - and of running a blacklist of media figures who were to be barred from receiving state support because they had been critical of her government.
March's impeachment ruling determined her actions had "seriously impaired the spirit of... democracy and the rule of law".
Is anyone else on trial?
Dozens of people have now been investigated or arrested in connection with the scandal. All have maintained their innocence.
Ms Choi, who also denies wrongdoing, has been on trial since December, while her daughter, Chung Yoo-ra - alleged to have received help getting a university placement - was arrested in Denmark in January.
The acting head of Samsung Group, Lee Jae-Yong, and four other Samsung executive are on trial for allegedly giving bribes to Ms Park and Ms Choi in exchange for government support for a controversial merger.
Former health minister Moon Hyung-pyo and the chief investment officer of the National Pension Service (NPS) Hong Wan-seon are on trial for allegedly pressuring the NPS to accept the merger.
And last week, two plastic surgeons who treated the image-conscious former president - including one who injected her with human placenta extracts - were convicted of lying about having treated her.