Chambers was born in Islington, and raised in Finsbury Park, London. Running was a part of his family life: his older sister Christine won the senior 100 metres Finals at the English Schools Championships in 1986 and 1987 and competed in the European Athletics Junior Championships. As a schoolboy he was coached by Selwyn Philbert who devoted himself to the young sprinter. Chambers first athletic success came at the 1994 English Schools' Athletic Association Championships, where he won the boys' intermediate 100 m race with a time of 10.64 seconds. International medals followed at the 1995 European Junior Championships, at which he won the 100 m and the 4×100 metres relay. He defended these titles at the 1997 European Junior Championships, and set a then world junior record in the 100 m with a time of 10.06 s.