Rudisha competed at the 2009 World Athletics Championships, reaching the 800 metres semifinals. In September 2009, Rudisha won the IAAF Grand Prix meeting in Rieti, Italy, posting a new African record of 1:42.01, beating the 25-year old record of 1:42.28 set by compatriot Sammy Koskei. That effort put him in fourth place on the all-time list. In the 2010 IAAF Diamond League, he took on Abubaker Kaki at the Bislett Games in June. He defeated Sebastian Coe's 31-year-old meet record with a run of 1:42.04, giving him another place in the top-ten fastest ever 800 m and leaving Kaki the consolation of the fastest ever non-winning time. On 10 July 2010, Rudisha ran the 800 m in 1:41.51 at the KBC Night of Athletics in Heusden, Belgium; this new personal record placed him No. 2 all-time in the world for the 800 m.
In November 2010, at the age of 21, he became the youngest ever athlete to win the IAAF World Athlete of the Year award. He also won the Kenyan Sportsman of the Year award.
With a time of 1:41.74, Rudisha set the United States all comers 800 m record at the 2012 adidas Grand Prix at Icahn Stadium in New York City. He guaranteed his selection for the Kenyan Olympic team for the first time with a win at the Kenyan trials, running a time of 1:42.12 minutes – the fastest ever recorded at altitude.
Rudisha currently holds the world record for the 800 m. He broke the record at the London 2012 Olympics on 9 August 2012, with a time of 1:40.91