Harold Walker was born 19 October 1932, the son of the late Admiral Sir Harold Walker, KCB, RN, and Lady Walker (née Berners); he was educated at Winchester and Worcester College, Oxford. In 1960 he married Jane, daughter of the late Captain. C. J. L. Bittleston, CBE, DSC, RN.

After serving as 2nd Lieutenant Royal Engineers, 1951-52., Walker entered the Foreign Office in 1955. His diplomatic career included: MECAS, 1957; Assistant Political Agent, Dubai, 1958; Foreign Office, 1960; Principal Instructor, MECAS, 1963; First Secretary, Cairo [Egypt], 1964; Head of Chancery and Consul, Damascus [Syria], 1966; Foreign Office (later FCO), 1967; First Secretary (Commercial), Washington [United States], 1970; Counsellor, Jedda [Saudi Arabia], 1973; Deputy Head, Personnel Operations Department, FCO, 1975-76, Head of Department, 1976-78; Ambassador to Bahrein, 1979-81, to United Arab Emirates, 1981-86, to Ethiopia, 1986-90, to Iraq, 1990-91. He retired in 1992.

Walker was awarded the KCMG in 1991 (CMG 1979).