Thomas Richardson was born 6 February 1941, son of Arthur Legh Turnour Richardson and Penelope Margaret Richardson. He was educated at Westminster School and Christ Church College, University of Oxford (MA (Hist.)). In 1979, he married Alexandra Frazier Wasiqullah (née Ratcliff).

Richardson joined the Foreign Office in 1962 and after a secondment to the University of Ghana, 1962-63, he served in the following posts: Foreign Office, Near East and North Africa Department, 1963-65; Third Secretary, Dar es Salaam [Tanzania], 1965-66; Vice-Consul (Commercial), Milan, 1967-70; seconded to N. M. Rothschild and Sons, 1970; FCO, Financial Policy and Aid Department, 1971-74; First Secretary, UK Mission to United Nations, 1974-78; FCO, Deputy Head of Energy, Science and Space Department, 1978-80; seconded to Central Policy Review Staff, Cabinet Office, 1980-81; Head of Chancery, Rome, 1982-86; Head of Economic Relations Department, FCO, 1986-89; UK Deputy Permanent Representative to United Nations, with personal rank of Ambassador, 1989-94; Deputy Political Director and Assistant Under-Secretary of State (Western Europe), FCO, 1994-96; Ambassador to Italy and (non-resident) to San Marino, 1996-2000.