Avihu was the second son of Aharon the Kohen and Elisheva, daughter of Amminadav and sister of Nachshon. His brothers were Nadav, the eldest, Elazar and Itamar. Together with his father and brothers he was consecrated to the priesthood and served in the Mishkan.

At the covenant at Sinai, Moshe was told to ascend with Aharon, Nadav, Avihu and seventy elders of Israel. The Torah relates that they saw the God of Israel, beneath whose feet was the likeness of a pavement of sapphire.

On the eighth day of the priests' installation, which Rashi identifies as Rosh Chodesh Nissan, the day the Mishkan was erected, Nadav and Avihu each took his fire pan and offered before God an alien fire which He had not commanded them. Fire came forth from before God and consumed them. They died without sons, and Elazar and Itamar served as priests in Aharon's lifetime.

The Sages offered various explanations of their sin. Rabbi Eliezer taught that they ruled on a point of law in the presence of their teacher Moshe; Rabbi Yishmael, that they entered the Sanctuary after drinking wine. Midrash Vayikra Rabbah lists further explanations.

The account of their death opens the Torah reading of Yom Kippur. The Midrash explains why: Rabbi Chiya bar Abba taught that Aharon's sons died on the first of Nissan, and their death is recalled on Yom Kippur to teach that just as Yom Kippur atones, so the death of the righteous atones.