The 80-year-old actor revealed the news in a statement to TV Guide magazine on Friday, assuring fans his cancer is highly treatable and he hopes it won't force him to pull out of the upcoming "Dallas" TV remake.
Hagman is confirmed to reprise his role as villainous oil tycoon J.R. Ewing in at least the first four episodes.
He says, "As J.R., I could get away with anything - bribery, blackmail and adultery. But I got caught by cancer. I do want everyone to know that it is a very common and treatable form of cancer. I will be receiving treatment while working on the new Dallas series."
He adds, "I could not think of a better place to be than working on a show I love, with people I love. Besides, as we all know, you can't keep J.R. down!"
A spokesman for Warner Horizon, the production company behind the new Dallas, adds, "Everyone at Warner Horizon Television and the entire Dallas family completely supports Larry Hagman during this time. We look forward to watching Larry once again work his magic by bringing one of television's most interesting, complex and controversial characters back to the screen in the new Dallas series."
It's not the first time the actor has battled a major health crisis - he underwent a successful liver transplant operation in 1995, having developed cirrhosis after years of heavy drinking.