[3] He reached the semifinals of the 400 m and won a surprise silver medal as a member of the Kenyan 4 × 400 m relay team at the 1968 Summer Olympics.

Nyamau won the gold medal in the 4 × 400 m relay at the 1970 British Commonwealth Games.

In September 1970, Nyamau - with teammates Naftali Bon, Thomas Saisi and Robert Ouko - set the men's 4x880 yard world record at 7:11.6.

At the Munich Olympic Games, Nyamau was eliminated in the quarterfinals of the 400 m, but he won the gold medal in the absence of the United States as a member of the Kenyan 4 × 400 m relay team.

Other members of the team were Charles Asati, Robert Ouko and Julius Sang.