Brooks made her screen debut in the silent The Street of Forgotten Men, in an uncredited role in 1925. Soon, however, she was playing the female lead in a number of silent light comedies and flapper films over the next few years, starring with Adolphe Menjou and W. C. Fields, among others.
She was noticed in Europe for her pivotal vamp role in the Howard Hawks directed silent "buddy film", A Girl in Every Port in 1928.
In an early sound film drama, Beggars of Life (1928), Brooks played an abused country girl on the run with hobos Richard Arlen and Wallace Beery whom she meets while riding the rails. Much of this film was shot on location, and the boom microphone was invented for this film by the director William Wellman, who needed it for one of the first experimental talking scenes in the movies.
By this time in her life, she was mixing with the rich and famous, and was a regular guest of William Randolph Hearst and his mistress, Marion Davies, at San Simeon, being close friends with Davies' niece, Pepi Lederer. Her distinctive bob haircut helped start a trend; many women styled their hair in imitation of her and fellow film star Colleen Moore. Soon after the film Beggars Of Life was made, Brooks, who loathed the Hollywood "scene", refused to stay on at Paramount after being denied a promised raise, and left for Europe to make films for G. W. Pabst, the prominent Austrian Expressionist director.
Paramount attempted to use the coming of sound films to pressure the actress, but she called the studio's bluff. It was not until 30 years later that this rebellious move would come to be seen as arguably the most savvy of her career, securing her immortality as a silent film legend and independent spirit. Unfortunately, while her initial snubbing of Paramount alone would not have finished her in Hollywood altogether, her refusal after returning from Germany to come back to Paramount for sound retakes of The Canary Murder Case (1929) irrevocably placed her on an unofficial blacklist. Actress Margaret Livingston was hired to dub Brooks's voice for the film, as the studio claimed that Brooks' voice was unsuitable for sound pictures.
Once in Germany, she starred in the 1929 film Pandora's Box, directed by Georg Wilhelm Pabst in his New Objectivity period. The film is based on two plays by Frank Wedekind (Erdgeist and Die Büchse der Pandora) and Brooks plays the central figure, Lulu. This film is notable for its frank treatment of modern sexual mores, including one of the first screen portrayals of a lesbian. Brooks then starred in the controversial social drama Diary of a Lost Girl (1929), based on the book by Margarete Böhme and also directed by Pabst, and Prix de Beauté (1930) by Italian author Augusto Genina, the latter being filmed in France, and having a famous surprise ending. All these films were heavily censored, as they were very "adult" and considered shocking in their time for their portrayals of sexuality, as well as their social satire.