 Alfred's major theoretical work was "Principles of Economics"; he is mentioned as the only author, but Mary may have done quite as much work as he did on the book.According to James and Julianne Cicarelli, who wrote a book entitled "Distinguished Women Economists", she was listed by John Maynard Keynes in his "Essays on Biography".The Cicarellis say that “Keynes held her in the highest regard and considered her an intellectual and thinker every bit as significant to the historical development of economics as her husband or any of the other economist about whom he wrote.”

After her husband died in 1924, Mary became Honorary Librarian of The Marshall Library of Economics at Cambridge, to which she donated her husband's collection of articles and books on economics.