Moorcroft made his senior debut for Great Britain in 1973 and competed in his first Olympic Games in Montreal 1976, placing seventh in the 1,500-metre final. He won gold in the 1978 Commonwealth Games in Edmonton at 1500 metres. Just four weeks later, he won the bronze medal at the same distance in the European Athletics Championships in Prague. In the 1980 Moscow Olympics, he suffered from stomach problems and was eliminated in the 5,000-metres semifinals.