Sjef Janssen did not start riding until he was 28. He had bought two young horses and wanted to learn to ride them – one, Orion, was his first Grand Prix horse. Sjef spent two years at a school in Belgium whose proprietors had studied at the Spanish Riding School and with Nuno Oliveira. During this time he rode seven hours a day.

Sjef represented Holland at the 1983 European Championships on Orion, and won a bronze medal at the 1991 Europeans on Olympic Bo.

In 2005 he was appointed coach of the Dutch team, having already trained the enormously successful Anky van Grunsven, who he married in 2005 in Los Vegas at the World Cup final. Sjef resigned as coach in 2012 and the following year was appointed as advisor to the Belgian dressage team.