Reuven was the firstborn son of Yaakov Avinu and Leah. According to tradition, he was born in Charan on 14 Kislev. His mother named him, saying, "For G-d has seen my affliction; now my husband will love me." The Torah also relates that he found dudaim (mandrakes) in the field and brought them to his mother.

After Rachel's death came the episode of Bilhah, which the Sages took care to understand without condemning Reuven. The Talmud cites Rabbi Shmuel bar Nachmani: "Whoever says Reuven sinned is mistaken"; he merely disturbed his father's bed, out of concern for the honor of his mother Leah.

When his brothers wished to kill Yosef, Reuven intervened: "Shed no blood! Cast him into that pit out in the wilderness," intending to rescue him and bring him back to his father. He was absent when Yosef was sold; according to the Midrash, he was occupied with sackcloth and fasting in repentance for his deed concerning his father. The Holy One, blessed be He, told him: "Never has a man sinned before Me and repented, and you are the first to initiate repentance."

Before his passing, Yaakov rebuked him while acknowledging his stature: "Reuven, you are my firstborn, my might and the first fruit of my vigor." The birthright passed to Yosef and leadership to Yehudah. Moshe later blessed him: "May Reuven live and not die." His descendants received their inheritance east of the Jordan.

According to the tradition cited by Chabad, Reuven moved to Egypt with his family and died there on his 125th birthday, 14 Kislev. The site of his burial is disputed, with traditions placing it in Hebron, Arbel, Egypt or Palmachim.