Gad was the son of Yaakov and Zilpah, Leah's maidservant. It was Leah who named him, exclaiming "Good fortune has come" (ba gad); the word gad means luck, mazal. He had seven sons, Tzifyon, Chaggi, Shuni, Etzbon, Eri, Arodi and Areli, who founded the clans of the tribe.

According to the Yalkut Shimoni and Rabbeinu Bachya, who cites Midrash Tadshe, Gad was born on 10 Marcheshvan, by tradition in the year 2196 from Creation, during Yaakov's stay in Charan. He died at the age of one hundred and twenty-five. Rabbi Chaim Palagi writes in Moed LeChol Chai that the day of Gad's birth is a day of good fortune for anyone undertaking an endeavour.

Yaakov blessed him: "Gad, a troop shall troop upon him, but he shall troop upon their heel." Rashi and Ramban read this as foretelling the tribe's role in the conquest: settled with Reuven east of the Jordan, Gad's warriors went at the head of the other tribes to conquer Canaan and then returned home without losing a man. Moshe in his blessing likened Gad to a lion ("he dwells as a lion"), and Rashi explains that tribes living on the frontier had to be mighty. Rashi understands the words "for there the lawgiver's portion is hidden" as alluding to the burial of Moshe Rabbeinu within Gad's territory.

According to Rabbi Nehorai in the Midrash, the prophet Eliyahu came from the tribe of Gad, of the inhabitants of Gilead. Sefer HaYashar relates that Gad was buried across the Jordan, in the inheritance Moshe had given his descendants; one tradition places his tomb in a mosque in the centre of the town of Es-Salt in Jordan.