Hau Giang Province, South Vietnam, late 1965
It's the middle of the war. A man named Daniel Ellsberg (Matthew Rhys) is at a campsite with other soldiers to observe any progress in the battle for his work at the Embassy. At night, the soldiers walk through the forest before they are shot at by unseen enemy soldiers.
On his flight home, Ellsberg speaks to Secretary of Defense Robert McNamara (Bruce Greenwood). He talks to the Chief of Staff regarding the progress in the war. According to Ellsberg, nothing has changed, which McNamara states means things are just getting worse. Upon landing, McNamara speaks to the press, lying to them and saying that things are getting better.
Ellsberg later sneaks out of the Pentagon with classified documents on the Vietnam War. He meets in secret with two of his colleagues as they make copies of the papers. Ellsberg reads them, and it reveals that four U.S. presidents (Truman, Eisenhower, Kennedy, and Johnson) were covering up certain facts regarding the war, contrary to what they had told the press.
Washington, D.C., 1971
Publisher Kay Graham (Meryl Streep) meets with a colleague as she is set to take her company, The Washington Post, public. Graham gets a call from the Chief of Staff to inform her that President Nixon does not want The Post to cover his daughter's upcoming wedding. Graham later meets with her managing editor, Ben Bradlee (Tom Hanks), to discuss this. Graham makes suggestions to Bradlee about expanding their coverage on certain topics to attract a wider demographic of readers.
Graham sits in a board meeting full of men to discuss the plans for taking the company public. One of her colleagues, Arthur Parsons (Bradley Whitford), expresses his own doubts (with Graham listening in the next room) in part because she's a woman and knows that the other men may not feel comfortable with having someone like her in charge. Parsons also mentions how Graham inherited the company after her husband Philip, the previous head publisher, committed suicide (which everyone refers to as an "accident").
McNamara later visits Graham in her home to inform her that the following day's paper may post something unflattering about him.
Bradlee sends an intern to the New York Times to find out what one of its journalists, Neil Sheehan, is preparing to write up. The intern sneaks in and comes back to The Post with a rough outline of the next day's cover page, involving McNamara. Bradlee and his mates are none too pleased.
The Times publishes a story on obtaining the Pentagon Papers with news on the White House's cover-up stories. While Graham has dinner with Times editor Abe Rosenthal (Michael Stuhlbarg) and his wife, Rosenthal's assistant walks over to his table to inform him that Nixon wants to take the Times to court over the story.
Post journalist Ben Bagdikian (Bob Odenkirk) works tirelessly until he can meet with Ellsberg. They finally arrange a meeting in a motel where Ellsberg provides Bagdikian with over 1,000 printed papers. Once Bagdikian obtains them, he informs Bradlee, and he gathers other Post journalists, including Meg Greenfield (Carrie Coon) and Howard Simons (David Cross), to sit and arrange the papers together for their story.
In anticipation of a potential backlash/lawsuit, Bradlee hires lawyers Roger Clark (Jesse Plemons) and Anthony Essaye (Zach Woods).
Graham sits with her daughter Lally (Alison Brie) as she expresses her feelings over publishing the story on the Papers, as well as having to run the company herself. Graham kept it going as a means to support her family after Philip's death, and Lally gives her mother support. Bradlee later shows up to inform Graham that they may indeed face legal action should they proceed with publishing the Papers. Graham makes up her mind and decides to go through with it.
The next day, The Post publishes their story, and the newspapers hit the streets. Soon, other news companies from different areas start to follow suit and publish the same story.
Graham heads to the Supreme Court for the hearing on the case against The Post and The Times. Later on, The Post gets a phone call, and Greenfield answers it. She announces to everyone that the court ruled in favor of The Post. She then mentions a statement from a justice who said that the court rules in favor of the governed, not the governors.
Bradlee meets up with Graham at the publishing station, and the two walk off together in friendly conversation.
We see Nixon in the White House talking to someone, informing them to ban anyone from The Post from ever going near the White House. Later, a security guard at the Watergate Hotel notices a break-in taking place.