He attended the Chouinard Art Institute in the 1930; after graduation he was hired as an assistant animator by the Walt Disney Studio.

Alvarado became the background painter for Chuck Jones, and his first screen credit was on the 1947 Pepé Le Pew short, "Scent-imental Over You."

Around 1971 Alvarado joined Hanna-Barbera as a layout artist; he worked on such series as The Pebbles and Bamm-Bamm Show (1971), Wheelie and the Chopper Bunch (1974), and many others.

Alvarado provided artwork for almost every Disney (Chip 'n Dale, Scamp), Warner Bros. (Tweety & Sylvester, Road Runner), Hanna-Barbera (Yogi Bear) and Walter Lantz (Andy Panda) licensed title.

He also illustrated comic book adaptations of the animated films The Rescuers, Robin Hood, and Gay Purr-ee.