Mullich's began working in video game industry in 1978 when his COBOL professor at California State University, Northridge hired him to work as a clerk and programmer at Rainbow Computing, an early computer store in the Los Angeles area.

Upon graduating in 1980 with a degree in computer science, Mullich joined Edu-Ware as a full-time employee, and as his first assignment created the adventure game The Prisoner.

[7] In 1991, he joined developer Interactive Support Group to create driving and action games for fifth-generation console systems CD-I and 3DO.

Van Caneghem hired Mullich in 1997 to lead the Heroes of Might and Magic III development team.

[10] With the financial demise of parent company The 3DO Company, Mullich left New World for software publisher Activision, where he worked on Vampire: The Masquerade – Bloodlines, a role-playing game based upon the Source engine.