Kumar started training in
pehlwani at the
Chhatrasal Stadium's
akhada at the age of 14. He was trained at the
akhada by Yashvir and Ramphal, later by
Arjuna awardee Satpal and then at the
Indian Railways camp by Gyan Singh and
Rajkumar Baisla Gurjar. After switching to
freestyle wrestling Kumar's first success came at the World Cadet Games in 1998 where he won the gold medal in his weight category, followed by a gold at the Asian Junior Wrestling Championship in 2000. Moving out of the junior competitions, in 2003 Kumar won the bronze medal at the
Asian Wrestling Championships and a gold at the Commonwealth Wrestling Championships. Kumar placed fourth at the
2003 World Championships, but this went largely unnoticed by the Indian media as he fared badly in the
2004 Olympic Games in Athens, placing 14th in the 60 kg weight class. He won gold medals at the Commonwealth wrestling Championships in 2005 and 2007. He placed seventh in the
2007 World Championships and won a bronze medal at the
2008 Olympic Games in Beijing. He won a silver medal at the
2012 Summer Olympics, becoming the first person to win two Olympic medals for independent India. Kumar was awarded the
Arjuna Award in 2006 and a coveted
Padma Shree by the Indian Government in 2011.
2008 Beijing Olympics Kumar lost to
Andriy Stadnik in the first round of the 66 kg freestyle wrestling event, leaving his medal hopes hinging on the
repechage. He defeated
Doug Schwab in the first repechage round and
Albert Batyrov in the second round. In the bronze medal match on 20 August 2008, Kumar beat
Leonid Spiridonov 3:1. Kumar disclosed that he had no masseur during the three bouts he won within a span of 70 minutes to take the bronze. The team manager Kartar Singh who is a former Asian Games medallist acted as the masseur for him between the bouts.
2010 World Wrestling Championships, Moscow At the
2010 World Wrestling Championships Kumar became the first Indian to win a world title in wrestling. He beat the local favourite
Alan Gogaev of Russia 3–1 in the finals in the 66 kg category.
2010 Commonwealth Games, Delhi Kumar won gold medal at the
2010 Commonwealth Games held in
Delhi on 10 October 2010. He beat
Heinrich Barnes 7–0 in the finals in the 66 kg freestyle wrestling category. The bout was stopped by the referee in the second round. Earlier, in the semifinals, Kumar defeated Famara Jarjou 3–0 within 9 seconds. In the quarterfinals, Kumar defeated Pakistani opponent Muhammad Salman 10–0 in 46 seconds.
2012 London Olympics Kumar won a silver medal after losing the final to
Tatsuhiro Yonemitsu. Earlier, he had entered the final amid some controversy by beating Kazakhastan's
Akzhurek Tanatarov in the semifinal. The Kazakh athlete claimed Kumar had bitten his ear, which was denied by the latter. Kumar was the
Olympic flag bearer for India at the opening ceremony. This win made him the first Indian to win 2 individual Olympic medals since India's independence.
2014 Commonwealth Games, Glasgow Kumar defeated
Qamar Abbas in the 74 kg final to win the gold medal at the 2014 Commonwealth Games in
Glasgow,
Scotland. He won in 107 seconds by
fall.
2018 Commonwealth Games, Gold Coast, Australia Kumar won gold in 74 kg category on 12 April 2018, Thursday, beating South Africa’s Johannes Botha in the final that lasted 80 seconds thus achieving a feat of winning 3 gold medals in 3 consecutive Commonwealth Games. ==International competition==