Born in Mytilene, Kenteris, a student of physical education, started practising athletics at age 10, and started running seriously about ten years later, when he moved to Thessaloniki. Kenteris specialised in the 200 m and 400 m races.
It was not until 1999 that Kenteris took part in his first major international tournaments; while he was eliminated in the 400 m heats of the indoor world championships he returned that summer as a 200 m runner at the outdoor World Championships. Kenteris won his heat # 5, defeating then 100 m world record holder Maurice Greene, but did not start the quarter-finals due to injury. As a result, few people had heard of Kenteris when he surprised by qualifying for the 200 m final at the 2000 Summer Olympics in Sydney. Although defending Olympic champion Michael Johnson and reigning World Champion Greene did not compete, nobody had included Kenteris in his list of medal favourites, despite his being the fastest European at 200 m that summer with a 20.25 seconds from June. But Kenteris raced to the gold medal, denying Britain'sDarren Campbell and Ato Boldon of Trinidad and Tobago. In doing so, Kenteris became the first White male to win a 200 metre sprinting medal at the Olympics since Pietro Mennea achieved the feat by winning gold at the 1980 Summer Olympics in Moscow.
He also won the 200 m title at the 2001 World Championships, after a season where he mostly stayed out of international competition. The following year, Kenteris completed his trilogy by also winning the European title in Munich in 19.85, his personal best.
For the 2004 Summer Olympics, Kenteris was one of the hopes of the home crowd for winning a gold medal in athletics, and favourite to light the Olympic flame. However, on the day prior to the Games, Kenteris and his training partner Ekaterini Thanou failed to attend a drug test. While they claimed to have been injured in a motorcycle accident – in a frantic attempt to return to the Olympic village for the test upon hearing the news in the media – an official Greek investigation would later find that the alleged accident had been staged. In the ensuing doping scandal, Kenteris and Thanou announced their withdrawal from the Games on August 18 after a hearing before the Disciplinary Commission of the IOC, for what they described to be "in the interests of the country."