In 1916 the MacMahon family moved to the upper west side of Manhattan and Aline enrolled in nearby Barnard College.

By graduation she had appeared in nearly every program the school had mounted during those four years, and found multiple suitors for her talents, including offers from the Provincetown Players, producer / actor Walter Hampden, and the Neighborhood Playhouse.

[11] After signing a long-term contract with Warners, Aline spent the rest of her career splitting time between New York and Hollywood in order to be with her husband, the Manhattan-based architect and city planner, Clarence Stein.

In the 1930s and 40s she was a critical darling (Walter Winchell called her "the very good actress"[12]), often cast as the acerbic comedienne with a heart of gold, or the long-suffering woman unlucky in love.

Screen World Presents the Encyclopedia of Hollywood Film Actors said that she "moved into character roles with ease as she became plumper and more motherly looking.

"[2] In 1922 MacMahon was a member of the Neighborhood Playhouse company in Manhattan, just as Konstantin Stanislavski's Moscow Art Theatre visited New York for a legendary tour.

Accolades poured in for the MAT's performances, and the executives of the Neighborhood Playhouse made arrangements to charter the first teaching class of the Method in America, which Aline attended with nine others.

Aline MacMahon took the tenets of the Method very seriously, and was the only member of that inaugural class to achieve popular success, having debuted the technique on stage in the fall of 1923, and as the first practitioner of it on film in 1931.

[16] The biography Aline MacMahon: Hollywood, the Blacklist, and the Birth of Method Acting was published in 2022 by University Press of Kentucky.