Beginning as a university rower, Parker first rowed internationally at the Pan American Games. He then went on to compete at the 1960 Olympic Games in the men’s single sculls where he finished fifth. 
Parker started coaching at Harvard University in 1961 and two years later he was promoted to men’s head coach where he remained for 51 years. During that time Parker led his crew to 22 undefeated seasons and 24 EARC Sprints varsity titles. 
Internationally, Parker coached crews for the 1964 Olympic Games through to the 1984 Olympics. His men’s eight finished second at the World Rowing Championships in 1967 and sixth at the 1968 Olympic Games in Mexico. Then in 1972 at the Munich Olympics the Parker-coached men’s eight took silver. At the first Olympic Games where women’s rowing was included, the 1976 Montreal Olympic Games, Parker coached the United States women’s eight to a bronze medal.  
A total of 52 of the Harvard students that Parker coached went on to become Olympians including Henrik Rummel (bronze, men’s four, London Olympics) and Beijing Olympians Cameron and Tyler Winklevoss. The Winklevoss twins were also part of Parker’s Harvard crew that raced at the 2004 World Rowing Cup in Lucerne where they made the A-final beating the British and French Olympic crews in the process. The Harvard crew then went on to compete at the Henley Royal Regatta where they finished second – a race that was featured in the movie, “The Social Network”.
Parker has been honoured for his contribution to rowing in many ways including Boston’s Community Rowing’s boathouse, which was completed in 2008, being named after him and in 2011 Parker was honoured with the USRowing Medal of Honour. Quoted by USRowing Parker stated, “Honours are not my thing. My thing is coaching. That’s what I get a real sense of satisfaction from.” 
Often described as a man of few words, Parker earned the utmost respect of his athletes who would take his few words as sacred. He believed that a lot of rowing was about working hard, rather than technique,  and this helped shape his coaching ways, “In rowing I found a sport that demanded some skill, granted, but placed a much higher premium on plain hard work and persistence,” Parker was quoted as saying. 
Parker shied away from retirement and coached to the very end. A week before he died Parker left hospital to go out in a launch to watch his 1980 Olympic crew go for a reunion row. 
Parker died after a two-year illness from cancer.