Petersen, who also served on the museum's board of directors, died Friday at her home in Beverly Hills after battling breast cancer, said a museum spokeswoman.
Born in New York on June 24, 1935, Margie McNally worked as a model before meeting her future husband. He proposed to her after their first date, and they were married in 1963.
Her husband, a former Hollywood publicist, made his fortune publishing Hot Rod, Motor Trend and other magazines. In 1994 the Petersens donated $5 million for the Los Angeles County Museum of Natural History to buy the old Ohrbach's department store building at the corner of Wilshire Boulevard and Fairfax Avenue so it could house the museum's collection of vintage cars and motorcycles.
The couple later gave large sums to support the Petersen Automotive Museum, including $25 million in 2000 to create a nonprofit foundation to care for the collection. Earlier this year, Margie Petersen made a gift through the Margie and Robert E. Petersen Foundation to the museum that totaled $100 million and comprised 135 cars, the building itself and cash.
Among the other Los Angeles institutions that benefited from the Petersens' philanthropy were the Music Center, the L.A. County Museum of Art, Children's Hospital and Cedars-Sinai Medical Center, as well as St. John's Health Center in Santa Monica and the Boys and Girls Clubs of Hollywood.
Margie Petersen also ran Scandia restaurant on the Sunset Strip from 1978 to 1985.
The couple suffered a tragic blow in 1975 when their sons Bob, 10, and Ritchie, 9, died in an airplane crash. Flying to Colorado for a Christmas skiing vacation, Petersen and her husband were passengers in one small plane and their sons in another. The pilot of the plane carrying the boys was unable to avoid bad weather and crashed in the Rocky Mountains.
Petersen, whose husband died in 2007 at 80, has no immediate survivors.