Flynn's film and television career began in 1954 in The Barefoot Contessa as "Lulu McGee". She played "Maggie Blake" in the Sherlock Holmes episode, "The Case of the Belligerent Ghost".
She made four guest appearances on Perry Mason in the early 1960s, including as "Agatha Culpepper" in "The Case of the Floating Stones", as Mrs. Nichols in "The Case of the Irate Inventor" in 1960, and as Sylvia Lambert in the 1963 episode "The Case of the Bluffing Blast".
Her final appearance was in 1966 in the "Case of the Golfer's Gambit" as Rolasie Hedrick. During the 1965–66 season of the soap opera Days of Our Lives she made five appearances as Anna Sawyer. She made her final television appearances in 1987 in Outlaws.
Theater
Flynn performed on Broadway beginning in the late 1920s.[5] She appeared on stage through 1952 in the following productions, the most successful of which ran for three months:
The Unsophisticates (December 30, 1929-January 1930) as Phyllis
Penal Law 2010 (April 18, 1930-May 1930) as Lucy Van Dam
Gasoline Gypsies (June 1931-June 1931) as Ruth Warren
Three Times the Hour (August 25, 1931-September 1931) as Hildah Lovering
The Moon in the Yellow River (February 29, 1932-April 1932) as Blanaid
American Dream (February 21, 1933-March 1933) as Celia, Amarylils
Man Bites Dog (April 25, 1933-May 1933) as Helen Lee
Biography (February 1934-February 1934) as Slade Kinnicott
Jigsaw (April 30, 1934-June 1934) as Julie
A Sleeping Clergyman (October 8, 1934 - November 1934) as Cousin Minnie
Mother Lode (December 1934-December 1934) as Julia Musette
Noah (February 13, 1935-March 1935) as Ada
One Good Year (November 27, 1935 - June 1936) as Anne
The Puritan (January 1936-January 1936) as Kitty
Marching Song (February 17, 1937-April 1937) as Rose Graham
Romantic Mr. Dickens (December 2, 1940 – December 7, 1940) as Dora Spenlow (Later Dora Winter)[6]
The Distant City (September 22, 1941 – September 23, 1941) as Edna Scott
The Grass Harp (March 27, 1952 – April 26, 1952) as The Baker's Wife
Despite the brief length of the stage productions, Flynn garnered some good reviews. The New York Times noted her appearance in the very short-lived (5 days) 1940 production of Romantic Mr. Dickens, a drama about the romances of Charles Dickens, and wrote that she "fit smoothly into this rather unorthodox picture of a literary tradition."[6] After beginning her work in film and television, Flynn continued work in theater, making appearances in such as Summer Voices at the Circle Theater in Los Angeles as late as 1977.[7]
Of her 1965 performance in the West Coast Repertory Company's troubled production of Long Day's Journey Into Night, the Los Angeles Times wrote "The one saving grace of the evening was the fine performance by Gertrude Flynn of Mary Tyrone".[8]