Ion G. Duca (1879 - December 30, 1933) was prime minister of Romania from November 14 to December 30, 1933, when he was assassinated for his efforts to suppress the fascist Iron Guard movement.

Born in Bucharest, he entered Romania's Chamber of Deputies for the National Liberal Party in 1907 and served in the cabinet from 1914. Appointed foreign minister in 1922, he was an avid supporter of the Little Entente, formed between Romania, Yugoslavia, and Czechoslovakia to fend off Hungarian expansionist claims (Hungary claimed Transylvania, which Romania had recovered after World War I) and prevent the Habsburg dynasty from returning to power in Central Europe.

In November, 1933, King Carol II asked him to head the government as prime minister in preparation for the December elections. In this capacity, Duca worked to keep the growing fascist movement in check, even outlawing their political arm, the Iron Guard. He was shot to death shortly after by Radu Constantinescu, an Iron Guard supporter.

Duca wrote extensive memoirs about his experiences as a cabinet minister during World War I.