It is a seven-sided coin, an equilateral curve heptagon of constant breadth (3 centimetres) and mass 13.5 grams.

The sides are not straight but are curved so that the centre of curvature is the opposite apex of the coin – this is an equilateral curve which allowed the coin to roll freely in vending machines.

It was of the same shape and size of the British coin of the same denomination, as both nations' pounds were pegged until 1979.

The millennium coin was the first decimal to feature words on it, the word DUBLIN in Roman script and ÁṪ CLIAṪ in Gaelic type, its equivalent in the Irish language.

The coin was withdrawn on the advent of the euro in 2002, with its last minting issue in 2000.