The wildly popular show, which is set in a country mansion in early 20th century England, wrapped up its second season on PBS Sunday.
Boreanaz is the star of Fox's "Bones," but is best-known for his portrayal of centuries-old Irish vampire Angel in "Angel" and "Buffy the Vampire Slayer."
The New York Post said he is a huge fan of "Downton Abbey" and would love to join the cast in Season 3 as an American cowboy mentioned in passing by two characters on the Season 2 finale.
"HIRE ME!:" Boreanaz said in a Twitter posting Monday.
"I'd like to be the American cowboy who shakes things up at 'Downton Abbey.' I'm open for a visit Mr. Fellowes," he said, referring to the show's writer and creator Julian Fellowes.
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