Jean Tatlock and J. Robert Oppenheimer likely met in Berkeley, California, through shared social and intellectual circles. Oppenheimer was a physics professor at UC Berkeley, and Tatlock was a student. Their shared intellectual curiosity and left-leaning political views likely drew them together.

Jean and Robert engaged in an intense and passionate love affair during these years. They shared deep intellectual discussions and explored their mutual interests in literature, poetry, and politics. This relationship was known for its intellectual depth and emotional intensity. However, Oppenheimer's reluctance to commit fully to marriage was a point of contention.

Oppenheimer married Katherine (Kitty) Puening Harrison in November 1940. This event marked a significant turning point in his relationship with Jean, though they continued to see each other intermittently.

Despite Oppenheimer's marriage, he and Jean maintained occasional contact. Their final documented meeting took place in June 1943, arranged during a time when Oppenheimer was deeply involved with the Manhattan Project. He visited her in San Francisco. This meeting later became a point of scrutiny during Oppenheimer's security clearance hearings.

After Jean’s passing, this relationship played a significant role in the security investigations related to Oppenheimer and his involvement with the Manhattan project. It was used as possible motivation for security risk. The nature of their relationship and her political associations were used to question his loyalty and suitability for sensitive positions. Oppenheimer was deeply affected by Jean's death.