Gusty winds in the stadium on Saturday evening 11 August, made conditions for the javelin throw less than ideal, and worse than during Wednesday's qualifying rounds. Walcott responded to the pressure of the Olympic finals by throwing a personal best distance on his first throw, giving him the lead, and then exceeding that distance on his second throw. He won the Olympic javelin gold medal with a throw of 84.58m (277 ft 6 in). He defeated a string of top athletes to win the competition including 90-metre thrower Tero Pitkämäki and two-time defending Olympic champion Andreas Thorkildsen, as well as Veselý, Oleksandr Pyatnytsya and Antti Ruuskanen. This made Walcott the youngest-ever Olympic champion in javelin throw and the second non-European to win the Olympic gold in men's javelin throw since American thrower Cy Young in Helsinki in 1952.
Walcott has been coached since 2009 by Cuban-born Ismael Lopez Mastrapa.
In 2010 he stepped up to the standard regulation javelin (800-gram), and he continued his domination of the Caribbean junior division, as the three-time winner in the Junior (under-20) javelin throw at the CARIFTA Games in 2010 to 2012, setting a new NACAC North, Central American and Caribbean junior record in 2012.
Walcott's 2013 season was hampered by injury. In his first competition since his Olympic victory, he "opened big", nearly matching his personal best with an opening round throw of 84.39 m (276 ft 10⁄4 in) at a hometown meet in Hasley Crawford Stadium in Port of Spain, Trinidad, on Friday 3 May.