Born and raised in Thornton Heath, London, the second of four children born to Marie and Liam Rooney Sr., Irish immigrants from Sligo and Westmeath, respectively, Rooney started running for Croydon Harriers just before starting his secondary school, The John Fisher School. He attended St James the Great Primary School, Thornton Heath where his mum teaches. As a result, he became an avid Crystal Palace F.C. fan. Initially training and competing at the middle distances; 800 metres and 1500 metres and doing cross country throughout the winter, Rooney's talent for the one lap sprint was discovered by coincidence when he stood in to make up points at a London fixture. Rooney was selected to represent Great Britain at the 2005 European Juniors, held in Lithuania in July of that year. He achieved the Silver Medal in the individuals and gold with the relay team and on his return home was then asked to make up the senior's 4 × 400 m men's relay team at the 2005 IAAF World Championships in Athletics, held that year in Helsinki, Finland. Martyn was originally running only in the heat, but impressing the GB coaches with a time of 44.9 seconds, he was selected to also run in the final. Despite completing his leg in 44.8 seconds, Martyn and team mates Timothy Benjamin, Robert Tobin and Malachi Davis came in fourth, with a sub three-minute time. Rooney represented England in the 2006 Commonwealth Games held in Melbourne, Australia. Despite impressing everyone throughout the heats, he came fifth in the final with a time of 45.51 seconds and set a new British Junior Record, previous held by Roger Black for 20 years. The English 4 × 400 m Men's relay team came in fourth at the Games. At the 2006 World Junior Championships in Beijing he finished third in 45.87 seconds. The British relay team too finished third, earning him a second bronze medal of the Championships. During 2008 Martyn had a successful season where he went comfortably under the 45-second barrier with a 44.83 at the London Grand Prix. At the 2008 Beijing Olympics, Rooney set a new personal best in the Semi-final and finished sixth in the final. He also anchored GB to 4th in the relay with a 43.7 split, second fastest ever by a Briton. It was announced on 13 September 2016 that the Russian athlete Denis Alexee, had failed a retest of his sample from the 2008 Olympics. This means that Rooney will be upgraded to a bronze medal from the 4x400m along with Michael Bingham, Robert Tobin and Andrew Steele. At the 2009 World Championships in Athletics, he reached the semi-finals of the 400 m, but finished seventh and did not compete in the final. Running with Conrad Williams, Michael Bingham and Robert Tobin, Rooney had greater success in the men's relay event, winning the silver medal behind the winning team from the United States. He started the 2010 outdoor season with a European leading time of 44.99 seconds to win at the Atletica Geneve Meeting. He went on to win bronze in the 400 metres at the European Championships in Barcelona. He won a silver medal in the relay. Rooney had a disappointing 2011, knocked out in the semi-finals of the 400 metres at the World Championships in Daegu and finishing eighth as part of the British team in the 4 × 400 m relay. In 2012 Martyn started well, running 44.92s in April at the Mt. SAC Relays in Walnut, California, his fastest time since 2008. Rooney was unable to sustain that form going into his home Olympics, and he was eliminated in the semi-final of the 400 metres, running 45.31s. In the 4 × 400 metres relay final Martyn received the baton in sixth place and ran a blistering 44.1 second anchor leg, but was just unable to overtake Deon Lendore of Trinidad and so finished fourth. In Moscow 2013, Martyn competed for GB in the 4 × 400 m relay, running 44.77 in the heats and 44.50 seconds in the final, where he switched from the 4th leg to the 2nd leg. In the 2014 Commonwealth Games Rooney competed in the 400m and made it through to the finals coming first, but came fourth in the finals with a time of 45.15. Rooney took his first individual European title in the final of the 400m at the 2014 European Athletics Championships in Zürich with a time of 44.71. In the 2017 World Athletics Championships in London, Rooney failed to qualify for the semi-final finishing 6th in his heat in a time of 45.75.
Personal life
Martyn is coached by , coach to Olympic Champion Christian Taylor amongst other World and Olympic medalists. Martyn is also coached by British Strength and Conditioning expert Michael Johnston. He is married to former British pole vault record holder Kate Rooney. In August 2015, their first child, a son, was born. Their second, a daughter was born in August 2017.
