At the 1993 World Championships in Athletics in Stuttgart he finished second after a controversial incident on the final lap in which he lost one shoe after making contact with the eventual winner Haile Gebrselassie. He also won the 100th Boston Marathon in 1996 as well as the 102nd Boston Marathon in 1998. Tanui won IAAF World Half Marathon Championships in 1995 and silver in the 1997 competition.