Leslie C. Nelson, Jr. grew up in New Brunswick, New Jersey. After high school, he joined the Army and served in the European Theater during World War II. Nelson was awarded a Purple Heart. He attended Rutgers and graduated with a degree chemistry in 1949. There he was a member of Scarlet R, a past president of the Rutgers Touchdown Club, and a Loyal Son of Rutgers. After Rutgers, he worked for the New Brunswick Research Laboratory of the U.S. Atomic Energy Commission and became the executive director.