William Tanui first became noticed relatively late in life, when he won the 1,500 metres at the Kenyan Commonwealth Games trials in 1989, but he ran only sixth at the 1990 Commonwealth Games. In the same year he won the 800 m at the African Championships. At the 1991 World Indoor Championships, Tanui crossed the line first but was disqualified for breaking from his lane early. Tanui's greatest moment came at the 1992 Olympics in the 800 final when he stormed down the outside, finishing in lane 3, to narrowly beat his countryman Nixon Kiprotich for the gold. Tanui was unable to repeat this form in his only appearance at a World Championships, at Stuttgart in 1993, placing seventh. Tanui concentrated more on the 1,500 later in his career and finished fifth at that distance in the 1996 Olympic Games in Atlanta. At the World Indoor Championships he finished third in the 1,500 m in 1997 and fourth in 1999.
Personal Bests: 800 – 1:43.30 (1991); 1500 – 3:30.58 (1997).