Although he played stereotypical Latinos, Leo Carrillo was part of an old and respected Californio family who could trace his roots back to the conquistadores. His great-grandfather was the first provisional governor of California, and his grandfather Pedro Carrillo had been sent east to be educated in Boston. The family moved from San Diego to Los Angeles then to Santa Monica, where Leo Carrillo's father served as the city's first mayor. Proud of his heritage, he wrote a book titled The California I Love that was published just before his death in 1961.

A college graduate, Leo Carrillo worked as a newspaper cartoonist before turning to acting on Broadway. In Hollywood, he appeared in more than 90 films in which he played supporting or character roles. However, he is best remembered from the television show, the "Cisco Kid", on which he played Pancho, a role he had previously carried out in several films. As sidekck to Duncan Renaldo, the TV series ran from 1950 until 1956.

A preservationist and conservationist, Carrillo served on the California Beach and Parks commission for eighteen years, and played a key role in the state's acquisition of Hearst Castle at San Simeon, the Los Angeles Arboretum, and the Anza-Borrego Desert State Park. He was eventually made a goodwill ambassador by the State Governor.

As a result of his service to the State, the Leo Carrillo State Park, west of Malibu on the Pacific Coast Highway, was named in his honor, And the city of Westminster, California named an elementary school for him. The Leo Carrillo Ranch Historic Park in Carlsbad, California is a registered California Historical Site.

Leo Carrillo died of cancer in 1961 and was interred in the Woodlawn Memorial Cemetery in Santa Monica.

For his contribution to the motion picture industry, Leo Carrillo has a star on the Hollywood Walk of Fame at 1635 Vine Street.