The accident happened Friday afternoon, shortly after Thom, a New York City resident, picked up her motorcycle from storage in Yonkers, her nephew, Thom Loubet, told The Journal News, White Plains, N.Y.
She was hit by a car and died at the scene.
"She's been riding motorcycles for probably 40 years," Loubet said.
Thom became the editor of Ms. in 1972 and remained with the magazine until her death, The New York Times reported.
She also authored several books, including a history of Ms. magazine, and co-edited an oral history of congresswoman and feminist leader Bella S. Abzug.
"Ms. Magazine, the Women's Media Center, the women's movement and American journalism have suffered an enormous blow," Robin Morgan, Jane Fonda and Gloria Steinem, the founders of the center, said in a statement Saturday. "Mary was and will always be our moral compass and steady heart."