At the Diamond League event in Paris on 6 July 2012, Greene ran a personal best of 47.84 secs in finishing second to Javier Culson to move even closer to the British record in the 400m hurdles. Greene was selected to captain the Great Britain athletics team for the 2012 London Olympics, as one of the favourites for a medal. In the first round of the 400 m hurdles Greene won his heat in 48.98s, the fastest time of round. In the semi-finals Greene ran sluggishly, finishing fourth and only qualifying for the final as a fastest loser. In the final Greene finished fourth behind 2004 Olympic champion Félix Sánchez, surprise American Michael Tinsley and Javier Culson, running slower than he had in the semi-final. Post-race Greene admitted huge disappointment, and blamed disruption to his training caused by a knee injury in the winter. Greene also ran in the final of the 4 × 400 metres relay, as the British team finished fourth, just 0.13 seconds off a medal.