Morgan Goronwy Rees (29 November 1909 – 12 December 1979) was a Welsh journalist, academic and writer.

Rees was born in Aberystwyth, the son of Apphla Mary James and Richard Jenkyn Rees, a minister of the Tabernacle Calvinistic Methodist Church, and a younger brother of judge Richard Geraint Rees. The family later moved to Roath, Cardiff, and Goronwy was educated at Cardiff High School for Boys. He received three scholarships in 1927 to attend New College, Oxford, where he studied History. In 1931 he became a Fellow of All Souls College.

After leaving university, Rees wrote first for the Manchester Guardian. In 1936, he became assistant editor of The Spectator, for which he travelled to Germany, Russia, Spain, and Czechoslovakia. Though a Marxist during most of the 1930s, the Hitler-Stalin Pact turned him from communism and led him to enlist before the UK entered the war. During World War II, he joined the Royal Artillery and rose to second lieutenant in the Royal Welch Fusiliers. By 1943 he had risen further to the rank of Major on the staff of Lieutenant General Sir Frederick Morgan, COSSAC (Chief of Staff to the Supreme Allied Commander), the office responsible for planning Operation Overlord. After the army, he resumed work at The Spectator. In 1946, he became an administrator for H. Pontifex & Son and may have started working for MI6. Rees's daughter confirms that he worked for MI6 then and until at least 1949: "and in the afternoons he went to 54 Broadway, next door to St. James's Park tube station, the offices of SIS (or MI6), where he worked for the Political Section which [...] assessed and evaluated information".

In 1953, Rees became principal of the University College of Wales in Aberystwyth. In 1956, a series of articles appeared in The People that described their anonymous author as a "Most intimate friend, a man in a high academic position". Guy Burgess appeared in them as a corrupt man, spy, blackmailer, homosexual, and drunk. The Daily Telegraph then revealed Rees was author. The university held an inquiry into the matter. Despite student support, university staff did not support him. Rees resigned before the inquiry ended, thus also ending his academic career. The inquiry's report was very critical of Rees. Moreover, "It turned out that a great many old acquaintances of Burgess and [Donald] Maclean were much more horrified – felt, indeed, much more betrayed – by the fact that the late Goronwy Rees gave a version of their flight to the People than by the flight itself. When Stephen Spender showed the Daily Express a friend’s letter about Burgess, he was held to have disgraced himself."

Rees sat on the Departmental Committee on Homosexual Offences and Prostitution and played an influential role in getting gay men's testimony heard. He spent the last years of his life in Aberystwyth. He wrote a column (signed "R") on current political affairs for Encounter. He also wrote two autobiographies, A Bundle of Sensations (1960) and A Chapter of Accidents (1972).

Rees appears under the name "Eddie" in Elizabeth Bowen's 1938 novel The Death of the Heart (Victoria Glendinning Elizabeth Bowen: Portrait of a Writer).

Michael Williams portrays Rees in the 1985 television movie Blunt: The Fourth Man.

Rees died of cancer on 12 December 1979 at Charing Cross Hospital in London.