The discovery of iridium is closely related to platinum and other platinum group elements. People of ancient Ethiopian and South American cultures have used naturally occurring platinum metal since ancient times, which must contain small amounts of other platinum group elements, including iridium. The 17th century Spanish conquistadors discovered platinum in what is today the Colombian province of Chocó and brought it to Europe. However, it wasn't until 1748 that scientists discovered that it was not an alloy of any known metal, but an entirely new element.

Many high melting point oxide single crystals are grown in crucibles made of pure iridium. Pure iridium, platinum-iridium alloys, and iridium-rhodium alloys are mostly used to make scientific instruments, thermocouples, resistance wires, etc. Adding iridium to platinum can improve the corrosion resistance of platinum in water, acid, halogen, and mechanical strength below 500 °C, but with the increase of iridium content, the oxidation weight loss of the alloy in air above 900 °C also increased. The platinum-iridium alloy containing 10% iridium and 90% platinum is used to make the international standard meter ruler due to its extremely small expansion coefficient. The world's kilogram prototype was also made of platinum-iridium alloy.