Jacobs is 1.75 meters tall, which is close to the average height for American males. His parents were James Jacobs, a talent agent for the William Morris Agency, and Angela Jacobs, a homemaker. Tragically, Jacobs' father passed away from ulcerative colitis when Marc was just seven years old. This early loss had a significant impact on his upbringing.

Following her husband's death, Angela remarried multiple times, but these relationships were reportedly unstable. Marc has spoken in interviews about the challenges he faced during his formative years. He moved frequently across various New York City boroughs due to his mother's changing relationships. Over time, his family dynamics grew strained, and both his mother and siblings became less involved in his life, concerned that he lacked direction.

Jacobs eventually moved in with his paternal grandmother, who played a pivotal role in his development. It was she who introduced him to the world of fashion and nurtured his early interest in design and style. Despite battling ulcerative colitis—a condition he inherited from his father—Jacobs has managed to keep his health under control.