The eldest son of Robert the Steward (the future Robert II) and Elizabeth Mure, he was legitimated by their marriage several years after his birth. In 1362–63 he joined his father in a futile revolt against King David II, who both imprisoned him and created him earl of Carrick in 1368. (He had been created earl of Atholl in 1367.) Robert II became king in 1371; in 1384, because of his advanced age, he turned over the government to Carrick. After his injury in 1388, however, Carrick was supplanted by his brother Robert, earl of Fife.

On his accession, probably on April 19, 1390, he changed his name to Robert (III) from John, to avoid reminding others of John de Balliol, king of Scotland from 1292 to 1296, who was not favourably remembered. Fife, created duke of Albany in 1398, continued to govern throughout this reign, except for three years (1399–1402) when Robert III's eldest son, David, duke of Rothesay, took his place. The dissolute Rothesay died in March 1402 while imprisoned in Albany's castle of Falkland, Fife. Perhaps in an attempt to save his remaining son, James (afterward James I, king of Scots), from death at Albany's hands, Robert III sent the boy to France, but James was captured by English sailors, a shock to the aging king.