Jebb entered the Foreign Service in 1924, served in Tehran, where he became known to Harold Nicolson and to Vita Sackville-West and in Rome, as well as at the Foreign Office in London where, amongst other positions, he served as the Private Secretary to the Head of the Diplomatic Service.
In 1960 Jebb was made a hereditary peer and as Baron Gladwyn became involved in politics as a member of the Liberal Party.
Jebb's wife, Cynthia, Lady Gladwyn, was a noted diarist of their times in Paris and a hostess of Liberal and London politics.