Allwyn was born in South Manchester, Connecticut,[1] part of a family that included four sisters and a brother.

[2] At age 13, she sang well enough in a concert to be offered a scholarship to the Boston Conservatory of Music, but she declined rather than move away from her home.

[3] Allwyn studied dancing and dramatics in New York and later joined a stock company.

[3] In films, she often played the woman from whom the male star escaped, for example Charles Boyer's character's fiancée in the 1939 version of Love Affair or James Stewart's mentor's daughter in Mr. Smith Goes to Washington.

Her first husband was actor Robert Kent; the two appeared together in the 1936 Shirley Temple film Dimples.