"A year ago, tragedy struck at the 117th Boston Marathon. Four innocent people were killed that week, and hundreds more were wounded. Today, we remember Krystle Campbell, Lingzi Lu, Martin Richard, and Sean Collier. And we send our thoughts and prayers to those still struggling to recover," Obama said in a statement.
"We also know that the most vivid images from that day were not of smoke and chaos, but of compassion, kindness and strength: A man in a cowboy hat helping a wounded stranger out of harm's way; runners embracing loved ones, and each other; an EMT carrying a spectator to safety," he said.
"One year later, we also stand in awe of the men and women who continue to inspire us - learning to stand, walk, dance and run again. With each new step our country is moved by the resilience of a community and a city," he said.
"And when the sun rises over Boylston Street next Monday - Patriot's Day - hundreds of thousands will come together to show the world the meaning of Boston Strong as a city chooses to run again," Obama said.
"Just as we did in the years after 9/11, today we honour the victims of the Boston Marathon bombing by continuing to live our lives and proving that these cowardly acts do not deter the American spirit.
"That is why I am encouraged that this year's race will continue undeterred - a powerful symbol that the city of Boston and our nation have emerged from this tragedy stronger than ever," he said.
"I remember walking through Boston and the streets of Watertown with officials who risked their lives to save countless others, and who prevented another potential plot in New York City.
"While some wounds may never heal completely, it is the selflessness and bravery of those who ran towards the blasts to help their fellow citizens, instead of away, who give us hope and strength moving forward," McCaul said.