In 1931, Knowlden's father got her a screen test for the
Paramount Pictures film
Women Love Once while the whole family was visiting Hollywood for reasons related to Robert's work. He had called Fred Datig, a casting director at Paramount. Despite her young age, she managed to handle a speaking part with many lines without any problems. Due to child labor laws at the time, the family had to get permission for her to be able to work. They survived a car accident that day. Knowlden worked steadily in films, many high-budget ones, throughout the 1930s. She was often cast as the daughter of the main characters, or as the leading lady in her childhood. Looking like a younger version of the actress cast as the leading lady was often a major reason why she was cast in a certain role. Unlike most actors, children and adults alike, during the
studio system era, she was
never contracted to a particular studio. Apart from a temporary period during the filming of
Marie Antoinette when she studied at
Metro-Goldwyn-Mayer's Little Red Schoolhouse, she went to public school instead of schools for child actors in Hollywood. By 1934, Knowlden was seen as one of the few child actors to have established herself in a competitive industry. She was one of three actresses to portray Jessie Pullman (at age eight) in the 1934
Universal Pictures film
Imitation of Life. Over 100 children had auditioned for the part that she ultimately got. The film, based on
Fannie Hurst's 1933
novel of the same name, dealt with the topic of
passing (a theme that would again be explored in a film that she appeared in a couple of years later,
Show Boat). She played
Rochelle Hudson's character as a child. It was nominated for an Academy Award for Best Picture at the
7th Academy Awards the next year. In 2005, the film was selected for preservation in the United States
National Film Registry for being deemed "culturally, historically, or aesthetically significant". Knowlden appeared in two Academy Award-nominated films for
Best Picture the following year,
David Copperfield, and
Les Misérables.
David Copperfield was based on
Charles Dickens' 1850
novel, directed by
George Cukor, and released by MGM. It was
Freddie Bartholomew's debut in Hollywood. She played David's
foster sister Agnes Wickfield as a child. Despite both being cast in the same film, she never met comedic actor
W.C. Fields on the set. Her piano playing can be heard in one scene.
Les Misérables, directed by
Richard Boleslawski, was based on French author
Victor Hugo's 1862 novel
of the same name. Having both played the same character in
Imitation of Life, Knowlden and
Rochelle Hudson did it once again in
Les Misérables when they portrayed
Cosette during different moments of the film. Knowlden's face can be seen on most
DVD covers of the film, which starred
Fredric March and
Charles Laughton. Her performance was described as "memorable" and "excellent" by various newspapers. She would be cast in another one of Boleslawski's films,
Metropolitan, later that year. She was cast in
Rainbow on the River (1936), starring
Bobby Breen, one of the few
children's films that Knowlden ever appeared in. A reviewer from
Detroit Free Press lauded her performance as Lucille Layton, calling her "a fine little actress". In the 1938
historical drama film Marie Antoinette, she portrayed princess
Marie Thérèse of France, daughter of the title character, which was played by
Norma Shearer. Knowlden was considered for the role of "Careen O'Hara",
Scarlett O'Hara's youngest sister, in
Gone With the Wind, which ultimately went to
Ann Rutherford. ==Later life and death==