Upon his retirement from the Foreign Office, Vallat joined the faculty of King's College London, retiring with the rank of professor in 1976. Between 1973 and 1981 he was a member of the United Nations International Law Commission, and was its chair between 1977 and 1978.[2]
Vallat was appointed Queen's Counsel in 1961. He was appointed CMG in 1955, and promoted to KCMG in 1962. In 1982 he was appointed GBE.[2]