The threepence (3d) (Irish: leath reul) coin was a subdivision of the pre-decimal Irish pound, worth 1/80 of a pound or ¼ of a shilling. The Irish name (leath reul) literally meant "half reul", the reul being a sixpence coin worth the same as the Spanish real (a quarter of a peseta). As with all other Irish coins, it resembled its British counterpart, as the Irish pound was pegged to the British pound until 1979.

Originally it was struck in nickel and was very hard-wearing. In 1942, as nickel became more valuable, the metal was changed to cupronickel of 75% copper and 25% nickel. The coin measured 0.695 inches (17.7 mm) in diameter and weighed 3.23995 grams; this did not change with cupro-nickel coin. The coin was minted at the Royal Mint starting from 1928, and ceased to be legal tender after decimalisation on 31 December 1971. Ireland did not adopt the brass, dodecagonal three pence coin that Britain used between 1937 and 1971.