In many ways, the ceremony was a passing of the torch to a younger generation with speeches marked by fierce rhetoric over the nation's economic disparities.
Thousands gathered at the memorial site, some as early as 5 a.m., to hear President Barack Obama, King's children and other civil rights leaders. Speaker after speaker invoked King's "I Have a Dream" speech from 1963 to challenge others to carry on his fight.
"Yes, my father had a dream. It was a dream, he said, that was deeply embedded in the American dream," said King's son Martin Luther King III. "The problem is the American dream of 50 years ago [...] has turned into a nightmare for millions" who have lost their jobs and homes.
The nation has "lost its soul," he said, when it tolerates such vast economic disparities, teen bullying, and having more people of color in prison than in college.
His sister, the Rev. Bernice King, reminded the crowd that just before her father's assassination in 1968, he was mobilizing a poor people's campaign to occupy the nation's capital until the economic system changed.
She said the postponement of an earlier dedication because of Hurricane Irene that was planned on Aug. 28, the 48th anniversary of her father's "Dream" speech, may have been an act of God.
"Perhaps the postponement was a divine interruption to remind us of a King that moved us beyond the dream of racial justice to the action and work of economic justice," she said. "Perhaps God wanted us to move beyond the `dream' into action."
Other speakers included union leaders, the Rev. Jesse Jackson and Andrew Young, the former Atlanta mayor and U.N. ambassador who was an aide to King. Young urged the crowd to vote for a president who has their interests at heart.
Actress Cicely Tyson said her contemporaries are passing the fight on to a new generation. She passed the microphone to 12-year-old Amandla Stenberg. The girl recalled learning about the civil rights movement in school and named four young girls killed in a 1963 church bombing in Birmingham, Ala.
"As Dr. King said at their funeral, `They didn't live long lives, but they lived meaningful lives,"' Amandla said. "I plan to live a meaningful life, too."
Some looked to Obama to carry on King's legacy.
Street vendors nearby sold framed photographs edited to depict King and the nation's first black president conversing together in the Oval Office, along with a wide swath of buttons, posters and other souvenirs showing King and Obama.
U.S. Rep. John Lewis of Georgia said Obama's election was "just a down payment" on King's dream. "We're not there yet," he said.
About 1.5 million people are estimated to have visited the memorial's 30-foot-tall statue of King and its granite walls where 14 of his quotations are carved in stone since it opened in August. The memorial is the first on the National Mall honoring a black leader.
The sculpture of King with his arms crossed appears to emerge from a stone extracted from a mountain. It was carved by Chinese artist Lei Yixin. The design was inspired by a line from the "Dream" speech: "Out of the mountain of despair, a stone of hope."
Obama, who was just 6 years old when King was assassinated, saluted the civil rights icon as a man who pushed the nation toward what it "ought" to be and who changed hearts and minds.
"He had faith in us," Obama said. "And that is why he belongs on this Mall: Because he saw what we might become."
"As tough as times may be, I know we will overcome," Obama said. "I know there are better days ahead."
The president, who credits King with paving his way to the White House, left a copy of his inaugural speech in a time capsule at the monument earlier in the day.
Many who crowded in to see the president and hear Aretha Franklin and Stevie Wonder sing chanted "four more years" when Obama arrived. And they said the talk of economic fairness resonated with their own lives.
Joyce Lansdown, 61, a retired federal worker from Chantilly, Va., brought her daughter and granddaughter to the ceremony. She was glad Obama and others mentioned the importance of caring for seniors during the economic downturn.
"My heart goes out to them," she said. "My momma is still living on her little Social Security check."
Patricia Johnson, 50, drove with her godfather's granddaughter from Twinsburg, Ohio, to see the president and King's family. "It seems that President Obama as a young president is following King's footsteps," she said. "I think we can continue to learn a lot from (King's) example."
Her young family friend, 13-year-old Faron Bouldin, wiped tears from her eyes as a recording of King's full "Dream" speech played on large TV screens after Obama spoke.
"It feels really important for me," Bouldin said of King's message.
Some 10,000 chairs set up in a field near the memorial site were all filled. Many others stood in overflow sections.
The August ceremony when the memorial opened had been expected to draw 250,000, though organizers anticipated about 50,000 for Sunday's event.
Violinist Miri Ben-Ari performed an original composition written for the event and the song "Bus Passed" with spoken word artists Poem-Cees. Poet Nikki Giovanni read her poem "In the Spirit of Martin."
Wonder, Sheryl Crow James Taylor performed in a concert after the dedication.
The Rev. Al Sharpton called for people from around the world to see the monument's "stone of hope."
"When you walk through, you see a man standing in a posture of faith," he said. "Faith that brought us from the back of the bus to the White House."
Before the dedication, the King siblings walked through the memorial plaza with Obama, first lady Michelle Obama, and their two daughters. Bernice King said her family was proud to witness the memorial's dedication and hope it will spur action to solve the nation's problems.
Echoing her father's words, she told the crowd, "One day we'll all be able to say `Free at last, free at last, thank God almighty, we are all free at last."
Brett Zongker can be reached at http://www.twitter.com/DCArtBeat