The individual who served as Prime Minister of the UK during the Great Depression was Ramsay MacDonald. He was the first Labour Party leader to become Prime Minister, serving from 1929 to 1935. His government faced significant challenges tied to economic turmoil and high unemployment resulting from the global financial crisis. Although he initially attempted to implement social reforms and public works programs, the severity of the Depression led to fiscal constraints and the eventual formation of a National Government, reflecting the political complexities and difficulties of the time.