Director Peter Jackson announced on Facebook that Humphries will play the role of the Goblin King.
"Barry is perhaps best known for his business and social connections as the long-time manager of Dame Edna Everage.
He has also been an ardent supporter of the rather misunderstood and unfairly maligned Australian politician, Sir Les Patterson," Jackson said referring to Humphries' alter egos Dame Edna Everage, a Melbourne housewife and Sir Les Patterson, a politically incorrect cultural attache.
"However, in his spare time, Barry is also a fine actor, and we're looking forward to seeing him invest the Goblin King with the delicate sensitivity and emotional depth this character deserves," Jackson wrote.
Also joining the cast of The Hobbit is Evangeline Lilly who will be playing the new character, the Woodland Elf, Tauriel.
Another recent signing is British comedian Stephen Fry who will play The Master of Laketown.
Jackson, who directed the Lord of the Rings trilogy, adds: "Evangeline and Barry, along with Welsh actor Luke Evans as Bard and Benedict Cumberbatch as Smaug, just about rounds out the major casting. I cannot wait to get stuck into these new scenes!"
With the first round of shooting over, The Hobbit has started scouting locations for the second block of shooting for which Humphries and Lilly will be joining the cast.
The $US500 million ($A474 million) Hobbit movies, a two-part prequel to blockbuster The Lord of the Rings trilogy, began filming in New Zealand in March.
Australian actress Cate Blanchett will return as Galadriel, Ian McKellen as Gandalf, Orlando Bloom as Legolas, Christopher Lee as Saruman, Elijah Wood as Frodo and Andy Serkis as Gollum.
