Born in London to Czechoslovakian parents, Peter Knapp started rowing at Bedford Modern School in 1967, where he also enjoyed archery and swimming. After going to the Royal Veterinary College in 1968 he joined the London University Boat Club. Knapp soon got a seat in the first eight and rowed at number five in the crew that won the 1968 Grand Challenge Cup at Henley. He retained his place when the same eight represented Great Britain at the Mexico Olympics. Knapp qualified as a veterinary surgeon in 1972 and eventually opened his own practice in the south London town of Carshalton.