Freleng was born to a Jewish family in Kansas City, Missouri, where he began his career in animation at United Film Ad Service. There, he made the acquaintance of fellow animators Hugh Harman and Ub Iwerks. In 1923, Iwerks' friend, Walt Disney, moved to Hollywood and put out a call for his Kansas City colleagues to join him. Freleng, however, held out until 1927, when he finally moved to California and joined the Walt Disney studio. He worked alongside other former Kansas City animators, including Iwerks, Harman, Carmen Maxwell, and Rudolph Ising. While at Disney, Freleng worked on the Alice Comedies and Oswald the Lucky Rabbit cartoons for producers Margaret Winkler and Charles Mintz.
Freleng soon teamed up with Harman and Ising to try to create their own studio. The trio produced a pilot film starring a new Mickey Mouse-like character named Bosko. Looking at unemployment if the cartoon failed to generate interest, Freleng moved to New York City to work on Mintz' Krazy Kat cartoons, all the while still trying to sell the Harman-Ising Bosko picture. Freleng was very unhappy living in New York and made the best of it until another opportunity opened for him. Bosko was finally sold to Leon Schlesinger, who would produce the series for Warner Bros. At first Freleng was reluctant to return to California when Harman-Ising asked him to work on the series. At the insistence of his sister Jean, Freleng soon moved back to California to work on Looney Tunes.
Harman and Ising left Schlesinger's studio over disputes about budgets in 1933. Schlesinger was left with no experienced directors, and therefore lured Freleng away from Harman-Ising to successfully fix cartoons directed by Tom Palmer which Warner rejected. The young animator became Schlesinger's top director, and he introduced the studio's first true post-Bosko star, Porky Pig, in the film, I Haven't Got a Hat (1935). Porky was a distinctive character, unlike Bosko or his replacement, Buddy.
As a director, Freleng gained the reputation of a tough taskmaster. His unit, however, consistently produced high-quality animated shorts under his direction.