He competed for the British West Indies at the 1960 Summer Olympics held in Rome, Italy where he won the bronze medal in the 800 metres. He then teamed up with Keith Gardner, Malcolm Spence and James Wedderburn to win the bronze medal in the 4 x 400 metres.
In 1962, he became the first Jamaican athlete to have the national flag flown in recognition of winning a gold when he won double gold in the 400m and 800m at the Central American and Caribbean Games held at Kingston's National Stadium.
At the Tokyo Olympics in 1964, representing Jamaica, he finished fourth in the 800m and the 4x400m relay. He broke the Olympic record for the 800m in the semi-finals but lost the bronze by less than one tenth of a second with 1:45.9, his fastest ever time.
On June 4, 2012, Kerr had a heart attack and underwent heart surgery at the University Hospital of the West Indies. He remained in the intensive care unit until he succumbed to complications. He had a wife, Fay Kerr, five children, Karyn, Margaret, Roger, Candice and William Kerr and seven grand children.