Culson competed in the 2012 Olympics in London on Friday, 3 August; Saturday 4 August, and Monday 6 August. In interviews from his barrio Playa in Ponce, Puerto Rico, his family reported they would be "glued to their TVs" awaiting the moment Culson made entry into the Olympic stadium. He was also selected to be the flagbearer for the Puerto Rico delegation during the Opening Ceremonies of the London Olympics. A local reporter stated that, for the ceremony, most businesses in his barrio Playa closed down and "the streets were deserted". Culson scored the best overall time in the first day of competition, winning the highly-competitive heat 5 with a time of 48.33 seconds, and advancing to the semi-finals. This race also recorded the second best time and qualified more athletes than any other heat. Culson won his semifinal over two-time Olympic winner Angelo Taylor running 47.93 seconds. On 6 August 2012 Culson won the bronze medal in the final of the 400 meter hurdles with a time of 48.10 seconds (less than a half-second behind the gold-medal time), winning Puerto Rico's first Olympic medal in 16 years and the first Olympic athletics medal for his country (all other Puerto Rican medals had been won in boxing).