Aaron was the son of Amram and Jochebed, the brother of Moses and Miriam, and the first priest of Israel. God appointed Aaron to be Moses' spokesman in his audiences with the unnamed Pharaoh of Exodus. As a symbol of his office, Aaron received a magical rod. He turned the rod into a snake - the first in a series of signs, by which he and Moses hoped to persuade Pharaoh to let the Israelites leave Egypt. Aaron also used the rod to call down three of the plagues that followed this first sign (polluting the Nile, frogs and gnats). God also caused the rod to blossom and bear ripe almonds, as a sign that Aaron's descendants would inherit the priesthood.

God summoned Aaron to be present when Moses received the Ten Commandments. But Aaron did not stay on Sinai. Instead he agreed to oversee the casting of an idol (a golden calf) for the Israelites who had rebelled against the authority of the absent Moses.

Aaron was generally a supporter of Moses, but took him to task for his marrying a Cushite wife. For this God rebuked Aaron (and Miriam). His role as priest was critical when he made atonement for the Israelites and stayed the plague that had followed the rebellion of Dathan and Abiram. Exodus and Leviticus give a detailed account of the vestments and duties of Aaron and of his sons.

Aaron's elder sons, Nadab and Abihu, died early but the younger pair, Eleazar and Ithamar, succeeded him in the priesthood. When Aaron was a hundred and twenty three, God instructed him to go up onto Mt. Hor, where he died. Aaron figures prominently in Exodus, Leviticus, Deuteronomy and Numbers, and is named in other books of both Old and New Testaments.