Colvin graduated from Oxford University with a Bachelor of Arts (Hons) in English literature and arrived in Australia in 1974. He began employment in January 1975 at the ABC's rock music station Double Jay (2JJ, now known as Triple J) as one of the foundation staff, initially working as a cadet journalist. While at 2JJ, he presented news, conducted interviews, and produced current affairs and documentary specials until 1978. With strong foreign language skills in French, Italian and Spanish, he was posted to the Canberra bureau and was appointed a television news producer. A year later he was one of the first reporters on "Nationwide", along with Jenny Brockie, Paul Murphy, and Andrew Olle.