The actor plays Randolph McCoy, a member of the McCoy family who are involved in a feud with the Hatfields during the 1880s.
Paxton said to New York Magazine of his new look on the show: "I grew a beard, yeah. Oh man, I called it 'The Growler'. I let it go all the way down my neck and everything else.
"It wasn't the most attractive beard, but, yeah, it was good for the part. I went for the yellow teeth [too] and the whole thing. I really thought, 'The more I can look like a beaver in this, the better'."
Paxton also shared how he got involved with the miniseries, which features Kevin Costner, Jena Malone, Tom Berenger and Matt Barr.
"When I called Kevin, because he was the producer, we kind of knew each other in passing, I always thought he had a good work ethic, and I thought, 'Here this is, his first big foray into television, it's in his wheel-house... this guy's gonna make sure that they do this right'," he explained.
"And then we talked about the idea of having to go to Romania to shoot, and he was saying it's kind of a hell of a statement that we have to leave our families and go halfway around the world to make this thing, but that's the economics of the day that we live in.
"And in a way, I think going to Romania might have added a certain flavour that we might not have been able to get if we shot it where it really took place."
Hatfields & McCoys will premiere on Monday, May 28 at 9pm ET on the History Channel.
