The 555-foot-high (170-meter) marble and granite obelisk, the tallest stone structure in the world, was praised by speakers at a ceremony as an enduring symbol of U.S. ideals.
U.S. Interior Secretary Sally Jewell and billionaire philanthropist David Rubenstein, who paid for half of the $15 million in repairs, were among the dignitaries who cut a ribbon at the reopening.
"We invite the public to once again enjoy the unparalleled view of our nation's capital from the top of one of the most iconic symbols of democracy in our country," Jewell told an applauding crowd of several hundred people on the monument grounds.
The monument, the tallest structure in Washington, suffered cracks, loosened stones and lost mortar when it was whipsawed by a 5.8-magnitude earthquake in August 2011.
The temblor sent terrified tourists fleeing from the observation deck 500 feet up, and opened cracks so wide that light shined through.
After engineers rappelled from the top of the monument to inspect the damage, the structure was shrouded in scaffolding for months as workers carried out repairs.
The job included 665 feet of crack repairs, almost three miles (5 km) of repointing mortar joints, hundreds of mortar patches and 52 stainless steel anchors, some of them visible from the observation deck.
Public tours of the monument to George Washington, the first U.S. president, resumed after the ceremony. People started to line up for tickets at 1:30 a.m. EDT and 600 tickets were snapped up in the hour after the 8:30 a.m. opening.
The reopening ceremony was emceed by television personality Al Roker and included "American Idol" winner Candice Glover singing "America the Beautiful," the Army's Old Guard Fife and Drum Corps, the Navy Band and a children's choir.
The monument reopened to the public at 1 p.m., when about nine tourists took the 70-second elevator trip to the observation section.
"It's magnificent, it's worth the wait, and it's nice to be part of history," said Joe Vizzini, a 72-year-old hair salon owner from Boca Raton, Florida, as he admired the 30-mile view.
The monument was completed in 1884 and draws about 600,000 visitors a year.