"Today, we recognize the incredible courage and leadership of so many Bostonians in the wake of unspeakable tragedy," Obama said in a statement. "And we offer our deepest gratitude to the courageous firefighters, police officers, medical professionals, runners and spectators who, in an instant, displayed the spirit Boston was built on — perseverance, freedom and love."
Obama said this year's race, scheduled for April 21, will "show the world the meaning of Boston Strong as a city chooses to run again."
Authorities say two ethnic Chechen brothers who lived in the former Soviet republic of Kyrgyzstan and the Dagestan region of Russia planned and orchestrated the marathon bombings on April 15, 2013.
Tamerlan Tsarnaev, 26, died following a shootout with police days after the bombings. Dzhokhar Tsarnaev, 20, has pleaded not guilty to federal charges and is awaiting a trial in which he faces a possible death sentence. Prosecutors say the brothers also killed MIT police Officer Sean Collier days after the bombings in an attempt to steal his gun.
Prosecutors have said Dzhokhar Tsarnaev left a hand-scrawled confession condemning U.S. actions in Muslim countries on the inside wall of a boat in which he was found hiding following the police shootout.
At the tribute, several survivors of the bombing alluded to their injuries but focused on the strength they've drawn from fellow survivors, first responders, doctors, nurses and strangers who have offered them support.
"We should never have met this way, but we are so grateful for each other," said Patrick Downes, a newlywed who was injured along with his wife. Each lost a left leg below the knee in the bombings.
Downes described Boston Strong, the slogan coined after the attack, as a movement that symbolizes the city's determination to recover. He called the people who died "our guardian angels."