Security was tight along the 26.2-mile route, with a long list of prohibited items for both runners and spectators. But that didn't deter over 32,000 people from running in the marathon.
Two pressure-cooker bombs went off near the finish line on April 15, 2013, killing three people and wounding more than 260 others. A moment of silence was held at the starting line at 8:45 a.m. ET to honor the victims.
"We're taking back our race," said Boston Marathon race director Dave McGillivray. "We're taking back the finish line.
The elite women's race began shortly after 9:30 a.m. ET. Rita Jeptoo of Kenya successfully defended her title, becoming the seventh three-time Boston Marathon champion. She finished the race in a record 2 hours, 18 minutes, 57 seconds.
In the men's race, American Meb Keflezighi has won with a time of 2 hours, 8 minutes, 37 seconds. He was the first American to win the men's race since 1983.
Keflezighi, an Olympic medalist and UCLA graduate, looked over his shoulder several times during the final mile. When the 38-year-old from San Diego realized he wouldn't be caught, he began pumping his fist and made the sign of the cross. As he was presented with the trophy and laurel wreath, "The Star-Spangled Banner" echoed over Boylston Street, where the explosions rang out a year ago.
"I came as a refugee, and the United States gave me hope," said Keflezighi, who wrote the names of the three dead on his bib along with that of the MIT police officer who was killed during the manhunt that paralyzed Boston.
Buses bearing the message "Boston Strong" dropped off runners at the starting line in the town of Hopkinton, where loud music blared from a pair of tree-mounted speakers.
Race organizers expanded the field from its recent cap of 27,000 to make room for runners who were prevented from finishing last year and for family and friends of those affected by the blasts.
"I showed up, I'm back, and I am going to finish what I didn't finish last year," said Mary Cunningham, 50, of St. Petersburg, Fla., who was stopped a mile short of the finish line by the explosions.
Joe Ebert, 61, of Hampton, N.H., cheered on his son-in-law near the spot in downtown Boston where the bombs went off. He was in the same area last year at the time of the attack.
"I wanted to be in this spot," said Ebert, who wore a jacket and medal from when he ran the race in 2010. "Just wanted to let them know that they can't beat us down. I think it makes us all stronger when something like that happens."
At 2:49 p.m., the time the bombs went off, a moment of silence was observed at the finish line. It was followed by some of the loudest cheers of the day as people whooped, clapped and rang cowbells.
Dzhokhar Tsarnaev, 20, is awaiting trial for the attack and could get the death penalty. Prosecutors said he and his older brother - ethnic Chechens who came to the U.S. from Russia more than a decade ago - carried out the attack in retaliation for U.S. wars in Muslim lands. Tamerlan Tsarnaev, 26, died in a shootout with police days after the bombings.
The Associated Press contributed to this report.