Fifty years ago this month, a massive crowd — more than 250,000 people, by some accounts — converged on D.C. by bus, train, plane and even foot for a march that made history. On Aug. 28, 1963, the throng gathered in front of the Lincoln Memorial for the March on Washington for Jobs and Freedom, a demonstration of unity and political energy that’s credited with helping pass 1964’s Civil Rights Act and 1965’s Voting Rights Act.

The peaceful demonstration — organized by A. Philip Randolph, the Rev. Martin Luther King Jr. and other civil rights and labor leaders — cemented D.C.’s spot as the protest capital of the world.

This year, events in D.C. will commemorate the pivotal day, including a march and rally on Saturday. The National Portrait Gallery honors King’s career and legacy, from the 1955 bus boycott he led in Montgomery, Ala., to his assassination in 1968, in “One Life: Martin Luther King Jr.,” a show of photographs and ephemera.

“Giving a fuller account of [King’s] life helps put the March on Washington and that speech in context,” says curator Ann Shumard, who will lead a tour of the show at the museum Wednesday at noon.

She walked us through one of the exhibit’s most evocative items: an original program from the march, during which King delivered his “I Have a Dream” speech.

Before the speeches, musicians including Joan Baez, Bob Dylan and Peter, Paul and Mary entertained the crowd. The march from the Washington Monument to the Lincoln Memorial began around 11 a.m. The official program started about 1:30 p.m., Shumard says.

1. National Anthem: Given last-minute changes, the program is not an exact representation of the final lineup, Shumard notes. For example, the national anthem was performed by opera singer Camilla Williams; Marian Anderson later sang “He’s Got the Whole World in His Hands.”

3. Opening Remarks: A. Philip Randolph, one of the main organizers of the march, emphasized in his speech: “We are not a mob.” A massive police force was assembled for the day, but despite government officials’ concerns, the march remained peaceful.

5. Tribute to Negro Women Fighters for Freedom: The widow of Medgar Evers, an activist assassinated that June, didn’t make it on time. Daisy Bates, who fought against segregation in Arkansas, spoke on behalf of female freedom fighters instead.

6. Remarks: Patrick O’Boyle, archbishop of Washington, insisted that civil rights activist [and now Congressman] John Lewis remove some incendiary language from an earlier draft of his speech, afraid it would incite violence. Lewis obliged.

7. Remarks: Video clips from labor union leader Walter Reuther’s speech — “a real barn burner,” Shumard says — are part of the Portrait Gallery’s exhibition.

8. Remarks: James Farmer, another march organizer, was stuck in a Louisiana jail on this day. He’d been imprisoned for protesting and refused to be bailed out. The Congress of Racial Equality’s Floyd McKissick spoke instead.

14. Selection: Mahalia Jackson performed “I’ve Been ’Buked and I’ve Been Scorned” (at King’s request) and “How I Got Over.” Five years later, the gospel legend would sing at King’s funeral.

16. Remarks: King was already a national figure in the civil rights movement by the time of the march, but “that speech, without question, takes him to a whole new level,” Shumard says. “It’s a landmark moment, not just in terms of what he says in the speech, but in the audience it reached.”

17. The Pledge: The March on Washington pledge, printed on thousands of postcards, called for nonviolent protest, peaceful assembly and redress through legal actions. Excerpts:

“I pledge that I will not relax until victory is won. I pledge that I will join and support all actions undertaken in good faith in accord with the time-honored Democratic tradition of non-violent protest, of peaceful assembly, and petition, and of redress through the courts and the legislative process.

“I pledge to carry the message of the March to my friends and neighbors, back home and arouse them to an equal commitment and equal effort. I will march and I will write letters. I will demonstrate and I will vote. I will work to make sure that my voice and those of my brothers ring clear and determined from every corner of our land.”

National Portrait Gallery, Eighth and F streets NW; through June 1, 2014, free; 202-633-8300. (Gallery Place)