Born in Pound, Wisc., Haggerty helped his family raise several wild animals, including a black bear, while he was growing up. He left home after high school to move to California and pursue acting.
Haggerty landed a couple of nonspeaking roles, and worked as an animal trainer and a stuntman before landing the role of mountain man Grizzly Adams in the 1974 movie The Life and Times of Grizzly Adams. He reprised the role for the TV offshoot, which aired from 1977 to 1978 on NBC. His other screen credits include appearances in Charlie's Angels, CHiPs and The Love Boat in the early 1980s. He most recently appeared in Axe Giant: The Wrath of Paul Bunyan and Dead in 5 Heartbeats, both of which were released in 2013, as well as on the show American Pickers.
Haggerty also continued working on the sets of various productions and as an animal trainer on films like Grizzly Mountain (1997) and Escape to Grizzly Mountain (2000).
Haggerty's wife of more than 20 years, Samantha, died in a motorcycle accident in 2008. He discovered he had cancer a few months ago when he underwent surgery for back pain, according to TMZ.