Donald Trump is the first US president to be indicted in criminal proceedings, which also happened as he is seeking the Republican nomination in 2024.
The specific charge is not known, but the grand jury investigation centered on a $130,000 bribe to porn actress Stormy Daniels to stop her from going public about a sexual encounter with Trump.
The key witness in the case, former Trump lawyer Michael Cohen, told MSNBC that the indictment "will speak for itself."
Trump is due to appear in court on Tuesday next week for his arraignment, during which he will be asked to enter a plea, according to his lawyer.
Trump described the indictment as "political persecution" and said he doesn't expect a fair trial.
Supporters waving US flags have gathered outside Trump's Mar-a-Lago estate in Florida, where he has been staying.
Longtime ally Sen. Lindsey Graham called the indictment "a shocking and dangerous day for rule of law in America."
Democrats say the indictment proves that no one is above the law.
There has been no statement yet from US President Joe Biden.
