Walker, the 1907 South African Champion, was not among the big favourites for the 100 m at the 1908 Summer Olympics. He even had trouble getting to London, as there weren't enough funds for that, until a Natal sportswriter collected funds to support Walker. In England, he was coached by Sam Mussabini, later also the coach of Harold Abrahams.
Several of the big names did not qualify for the final, but Walker did. There he competed against three North Americans, of which James Rector of the United States had equalled the Olympic Record in the heats, as had Walker. Beating Rector in the final by about a feet and half, Walker is still the youngest winner of the Olympic 100 m as of 2002 (at 19 years and 128 days).