Aaron married Elisheba, a daughter of Amminadab, who was of the tribe of Judah (Exodus 6:23; 1 Chronicles 2:10). They had 4 sons - Nadab, Abihu, Eleazar, and Ithamar.
When the time of the Exodus came, God sent Aaron (Exodus 4:14, 27-30) out to meet the returning Moses (who had just spent 40 years out in the Sinai with Jethro), to join with him in their assigned task. Aaron was to be the spokesman for Moses, who was unable to speak well, perhaps from stuttering (Exodus 6:30; 7:1-2,9-10,19). Although Moses was the leader, it was Aaron who did the actual speaking to Pharaoh through the events leading to the Exodus, and the crossing of the Red Sea.
Aaron was a faultless servant with his brother, at least at first. At Rephidim, when Moses overlooked the battle with the Amalekites from a nearby hill with the rod of God in his outstretched hand, it was Aaron and Hur (his brother-in-law, Miriam's husband), who held up Moses' tired arms until Israel's forces under Joshua won the battle (Exodus 17:8-13).
Aaron's greatest lapse in judgment occurred while Moses was away on the mountain receiving the Ten Commandments from God. For whatever reason, Aaron gave in to the people's demands, and made that now-infamous golden calf for the people to worship (Exodus 32:4). When Moses returned, Aaron was sternly rebuked, but was forgiven by God after Moses prayed for him. Aaron came very close to being killed for that incident (Deuteronomy 9:20)
Aaron was appointed directly by God to be the first high priest. He and his sons were consecrated to continue the priesthood through time (Leviticus 8 and 9).
Aaron again displayed a failure in good judgment at Hazeroth when he and Miriam spoke out against Moses for marrying a Cushite (Ethiopian) woman. Once again, The Lord vindicated Moses, and punished Miriam, who had led the minor rebellion, with leprosy (Numbers 12:1-16). After Aaron acknowledged his and Miriam's error, at the intercession of Moses they were forgiven by God.
Aaron's career seemed to blow hot and cold. He certainly had his low points (i.e. the golden calf), but overall he remained a steadfast ally of his brother. During the Korah rebellion, Aaron stood courageously with Moses (Numbers 16:1-50). Not long after that, the miraculous sprouting of his staff was used to demonstrate that he was indeed the high priest to those who were questioning his authority (Numbers 17:1-13). That staff was afterwards preserved in the Tabernacle (Hebrews 9:4)
Neither Moses nor Aaron were permitted to enter the Promised Land (See Heartbreak Mountain). Aaron was involved in the water-from-the-rock incident at Meribah (Numbers 20:8-13), and for that presumptuous disobedience to God's instructions both were not permitted to enter the Promised Land (Numbers 20:24).
Aaron died at Mount Hor after his priestly authority was transferred to his son Eleazar. He was 123 years old (Numbers 20:23-29, Deuteronomy 10:6, 32:50). The people mourned his passing for 30 days.
Aaron was a forerunner of Jesus Christ in his role as the high priest. His priesthood was a "shadow of heavenly things," and was intended to lead the people of Israel to look forward to the time when "another priest" would arise (Hebrews 6:20). See The Day Of Atonement.
Fact Finder: Which 2 of Aaron's sons lost their lives for offering "unauthorized fire"?