Ellenberger, 28, made the gigantic news official by using an equally gigantic pencil to ink his name on the dotted line.
UFC Senior Director of Public Relations Dave Sholler was so amused by the pencil Ellenberger used that he told the Nebraskan to bring it with him on his first press tour.
"@JoeEllenberger @EllenbergerMMA @ufc @AdamEllenberger welcome. And bring that pencil on your first press tour," Sholler tweeted.
Ellenberger also took to Twitter to thank his fans for the support, but he made no mention of the pencil.
"Overwhelmed with all of the love & support from #EllenbergerNATION & @ufc fans around the world. You guys are motivating! #blessed," Ellenberger tweeted after the announcement was made.
Gigantic pencil or not, it's hard to argue with the UFC's decision to sign him.
The twin brother of perennial welterweight contender Jake Ellenberger, Joe is a veteran of several high-level Midwest promotions, including Titan FC and Victory FC.
He rarely leaves his fights in the hands of the judges, as 12 of his 14 wins came by way of stoppage.
Most recently, Ellenberger knocked out former Strikeforce star Joe Wilk, who had been on a 7-1 hot streak.
Ellenberger, who holds eight MMA victories via knockout, is a former high school wrestling champion in his home state of Nebraska, and he's also a two-time NCAA Division II All-American wrestler.
The UFC hasn't yet announced who his first opponent with be.