Roberts announced the fight via his official Twitter account late Monday night.
UFC 125 takes place Jan. 1 at the MGM Grand Garden Arena in Las Vegas. The event is headlined by two championship matches: a lightweight title rematch between Frankie Edgar and Gray Maynard, and the first-ever UFC featherweight championship bout between Jose Aldo and Josh Grispi.
Roberts, who trains with Gilbert Melendez in California, will be seeking his third consecutive win in the UFC after beating Forrest Petz and Mike Guymon. Soto scored his first UFC victory at UFC 118 when he defeated Nick Osipczak.
UFC 125 MAIN CARD
Frankie Edgar vs. Gray Maynard (UFC lightweight title)
Jose Aldo vs. Josh Grispi (UFC featherweight title)
Takanori Gomi vs. Clay Guida
Nate Diaz vs. Dong Hyun Kim
Chris Leben vs. Brian Stann
UFC 125 PRELIMINARY CARD
Thiago Silva vs. Brandon Vera
Antonio McKee vs. Jacob Volkmann
Cole Miller vs. Matt Wiman
Daniel Roberts vs. Greg Soto
Phil Baroni vs. Brad Tavares