Mulder never played in a test match for South Africa. He was selected for the 1965 team as a totally unknown player after an outstanding performance during the Springbok trials on a wet field.

Based on this performance and the perception that the Springboks wil be confronted with wet conditions, in New Zealand, he was included in the 1965 touring side.

Mulder played in 11 tour matches and scored a total 20 points in a Springbok jersey.