In August 2009, Rimmer competed in the World Championships, held in Berlin. Rimmer looked promising throughout the heats of the 800 m, and after squeezing through his previous round he was well down the field in the semi-final in a time of 1:46.77. In July 2010, he became the first male 800 m runner in history to win five consecutive national senior titles in Birmingham. He won his first major championship medal in the European Championships in Barcelona, a silver medal behind Marcin Lewandowski with a 1:47.17.