During the depression, Hanna found an opening at Harman-Ising, the
Hollywood animation unit that made the original "Looney Tunes" and "Merrie
Melodies." By 1937, Hanna was hired by MGM as a director and story editor. Several weeks later, Joe Barbera came aboard as an animator and writer.

Hanna's precise understanding of comic tempo and his talent into an efficient unit were perfect complements - draftsmanship, strong storytelling sense and comic inventiveness § most enduring, successful partnerships in entertainment history.

Their first collaboration at MGM was "Puss the immortal "Tom and Jerry." To test the graphic d Boot,” Hanna and Barbera invented the pose reel, a series  of drawings photographed to give the illusion of movement.

For the next two decades, the producers were honored with seven Academy
Awards® for their famed cat-and-mouse team. They won additional acclaim for making cartoon characters dance with Gene Kelly in the motion picture "Anchors Aweigh" and "Invitation to the Dance," and dance with Esther Williams in "Dangerous When Wet."

Their success ended, however, when MGM, concerned by the advent of
television, eliminated the studio's animation department. Unemployed, Hanna and Barbera decided to make cartoons directly for the small screen, resulting in a new arena of original animation for television and a fresh stable of cartoon stars. Each had an unmistakable voice and character such as Huckleberry Hound, Yogi Bear, Quick Draw McGraw, Augie Doggie, Doggie Daddy, Snooper and Blabber.

In 1960, Hanna-Barbera expanded beyond advertising supported Monday
through Friday strip shows by producing the first-ever animated prime-time show with half-hour story lines. The perennially popular "The Flintstones” aired for six years and was followed by additional prime-time series, including "The Jetsons,” "Top Cat,” and "The Adventures of Jonny Quest." The studio ventured further into award- winning "Charlotte's Web" in 1973, "Heidi's Song" in 1982 and "Jetsons: The Movie” in 1990.

Over the years, Hanna-Barbera has changed ownership several times; the
studio was sold to Taft Broadcasting in 1967, and later became a division of Great American Broadcasting Company in 1988. Tumer Broadcasting System, Inc. (TBS) acquired Hanna-Barbera in late 1991.

Hanna was an executive producer on the full-length, animated, musical adventure, "Once Upon A Forest” featuring the voice talents of Michael Crawford and Ben Vereen, which was released in the Summer 1993 through Twentieth Century Fox. Hanna has also directed the ABC Specials " I Yabba Dabba Do You" and "Hollyrock-a-bye-baby" and served as an executive producer on the 1994 live-action movie “The Flintstones” from Universal Pictures. In October 1994. William Hanna and Joe Barbera were inducted into the Television Hall of Fame. In 1995, two original cartoon shorts directed by Hanna, "Hard Luck Duck" and “Wind-Up Wolf" debuted as part of Cartoon Network's "What A Cartoon!" project. These shorts marked his first directorial efforts since 1941.
In Spring 1996, William Hanna published his auto biography, A Cat Of Friends by Taylor Publishing Company.

Outside of work, Hanna enjoyed boating, barbershop singing and maintaining his ranch in Northern California. He was a charter member of the Boys Scouts of America.
Hanna lived in North Hollywood with his wife Vi, and has }
marriage/ family /child / therapist and David, CEO of a computer company.