Nine years ago, Henry's younger brother, Martin Richard, was one of three people who were killed when two bombs detonated near the Boston Marathon finish line on April 15, 2013. Martin was 8 years old at the time.
Henry told ABC Boston affiliate WCVB that he thought about his brother while running the course's 26.2 miles.
"I know if he was here, either this year or the next coming years, he would have been doing it with me. So that's all I could think about," Henry said.
Henry had his brother's name written in black marker on his right arm and his sister's name on his left arm for the occasion, he said. He also wore a yellow jersey with the word "Peace" written on it, underneath "Team MR8," the logo for the Martin Richard Foundation. The organization was launched in 2014 in Martin's honor, to promote the values of "inclusion, kindness, justice and peace," according to its website.
Before he reached the finish line, Henry also paused at the marathon's memorial with a teammate and after he crossed the finish line, he shared an embrace with his parents, Denise and Bill Richard, and his sister, Jane Richard.
"So many people were out there for me. All my friends, my family. Motivation was the least of my worries. There was so many people there to support me. It was wonderful and I couldn't believe it," Henry told WCVB.
Henry added that he would definitely run another Boston Marathon in the years to come.
"I loved every second of it and this feels so great, I can't wait to do it again," he said.
Monday's race was the 126th running of the Boston Marathon and passed through eight Massachusetts towns: Hopkinton, Ashland, Framingham, Natick, Wellesley, Newton and Brookline, before finishing on Boylston Street in Boston. The top finishers this year were Evans Chebet for the men's division, who clocked in at 2 hours, 6 minutes, 51 seconds, and Peres Jepchirchir for the women's division, who finished in 2 hours, 21 minutes, 1 seconds, ESPN reported.