James Rennell Rodd, 1st Baron Rennell was born in London on 9 November 1858, the son of Major James Rennell Rodd and his wife, Elizabeth Anne. Rodd was grandson of Vice-Admiral Sir John Tremayne Rodd and great-grandson of the geographer James Rennell. He was educated at Haileybury College and at Balliol College Oxford, where he won the Newdigate Prize in 1880.

Rodd joined the British Diplomatic Service and after various postings in Europe and Africa, was appointed in 1894 to the British Agency in Cairo as second-in-command to Lord Cromer. In 1897 he was sent as special envoy to Abyssinia (later Ethiopia) where he played an important part in negotiating an Anglo-Ethiopian Treaty with Emperor Menelik II. As Ambassador to Italy from 1908 to 1919, Rodd had a key role during WW1 in influencing Italy's decision to join with the Entente in 1915.

After retiring from the diplomatic service in 1919, Rodd served on Lord Milner's mission to Egypt in 1919 and was British delegate to the League of Nations between 1921 and 1923. He later sat as Conservative MP for St Marylebone between 1928 and 1932.

As well as his diplomatic and political career, Rodd was also a published poet, author and classical scholar. He married Lilias Georgina Guthrie in 1894 and they had four sons and two daughters. Rodd's eldest son, Francis, a banker and geographer succeeded him in the barony and his daughter, Evelyn Emmett, was a Conservative MP. James Rennell Rodd died in Surrey on 26 July 1941. Further details are given in the Oxford Dictionary of National Biography.