WASHINGTON - Donald Trump was indicted on felony charges Tuesday for working to overturn the results of the 2020 election in the run-up to the violent Jan. 6, 2021, riot by his supporters at the U.S. Capitol, with the Justice Department acting to hold him accountable for an unprecedented effort to block the peaceful transfer of presidential power and threaten American democracy.

The four-count indictment, the third criminal case against Mr. Trump, provided deeper insight into a dark moment that already has been the subject of exhaustive federal investigations and captivating public hearings. It chronicles a monthslong campaign of lies about the election results and says that, even when those falsehoods resulted in a chaotic insurrection at the Capitol, Mr. Trump sought to exploit the violence by pointing to it as a reason to further delay the counting of votes that sealed his defeat.

Even in a year of rapid-succession legal reckonings for Mr. Trump, Tuesday’s indictment, with charges including conspiring to defraud the United States government that he once led, was stunning in its al- legations that a former president assaulted the “bedrock function” of democracy. It’s the first time the defeated commander in chief, who is the early front-runner for next year’s Republican presidential nomination, is facing legal consequences for his frantic but ultimately failed effort to cling to power.

“The attack on our nation’s Capitol on Jan.6, 2021, was an unprecedented assault on the seat of American democracy,” said Justice Department Special Counsel Jack Smith, whose office has spent months investigating Mr. Trump. “It was fueled by lies, lies by the defendant targeted at obstructing a bedrock function of the U.S. government: The nation’s process of collecting counting and certifying the results of the presidential election.”

The Trump campaign called the charges “fake” and asked why it took two-and-a-half years to bring them.

Mr. Trump was the only person charged in Tuesday’s indictment. But prosecutors obliquely referenced a half-dozen co-conspirators, including lawyers inside and outside of government who they said worked with Mr. Trump to undo the election results. They also advanced legally dubious schemes to enlist slates of fake electors in battleground states won by Democrat Joe Biden to falsely claim that Mr. Trump had actually won them.

The indictment accuses the defeated president and his allies of trying to “exploit the violence and chaos” by calling lawmakers into the evening on Jan. 6 to delay the certification of President Biden’s victory.