He became interested in marine and underwater life when, at age 10, he peered through a pair of goggles in the waters off Redondo Beach, California.

He attended the University of Southern California on a football scholarship and earned a bachelor's degree in public administration in 1950.

He later earned additional degrees in Recreation Management, including a master of arts from Los Angeles State College in 1956.

He opened the world's first dedicated dive resort, The Underwater Explorers Society (UNEXSO) in Freeport, Grand Bahama Island.

Tillman co-founded the National Association of Underwater Instructors (NAUI), the first international SCUBA diving certification agency, with Neal Hess in 1960.