Born in St. Louis, Missouri, Andreas from a working-class Greek-American family. Attracted from early childhood to being on stage when at 4 his mother took him to see a community theater performance, he took theatre as an extra-curricular activity in high school. He then majored in it at St. Louis University, where he worked his way through school doing things like waiting on tables. Next, after earning a drama fellowship, Katsulas received a Master's Degree in Theater Arts from one of the nation's top schools for the genre, Indiana University in Bloomington, Indiana.

With never a doubt or hesitation, Andreas jumped right into the professional theater world, performing in plays in his native St. Louis with the Loretto-Hilton Repertory Theater. This was followed by work with the Theatre Company of Boston. After that, Katsulas moved to New York to some challenging off-off-Broadway theater at La Mama. This was followed by a fifteen-year heart and soul involvement with Peter Brook's International Theatre Company in Paris, performing around the world with a challenging combination of improvisational theater in every imaginable circumstance and space, and "prepared" theater pieces in traditional, as well as unconventional, theatrical spaces. Katsulas trod the boards from Lincoln Center in New York and The Kennedy Center in Washington, D.C., to the "mean streets" of Brooklyn and marketplaces in remote African Villages. There were performances from elite Theater Festivals in Iran, Avignon and Belgrade: in prisons & mental institutions; at rock quarries in Australia; on barrios in Venezuela; in sewage plants in Switzerland; winding through the streets of Venice, Italy; in the fields with farm workers in California, near the lakes of Minnesota with Native Americans, in sometimes extreme conditions like snow, rain, and intensive heat.

During a hiatus from the stage, a part in Michael Cimino's The Sicilian (1987) brought Andreas to Los Angeles, after which he was immediately cast as Joey Venza in Ridley Scott's Someone to Watch Over Me (1987), then as Arthur, the chauffeur, in Blake Edwards's Sunset (1988).

In early 2005, Andreas was diagnosed with inoperable lung cancer; he passed away a year later, in Los Angeles. He had lived there since 1986, and had hoped to return to working in the theater before his far-too-early death, just over three months shy of his 60th birthday.