The bout will take place at HP Pavilion in San Jose, Calif.
Thomson (19-5, one no-contest) last fought at a UFC-promoted event in August 2004. He was knocked out in the first round by Yves Edwards.
In his most recent outing, May 19, 2012, Thomson was on the short end of a split decision to Gilbert Melendez, who was the defending Strikeforce champion.
Thomson and Melendez faced each other three times for the Strikeforce 155-pound title; Melendez won two of those battles.
Strikeforce put on its final event Jan. 12 in Oklahoma City. Thomson, Melendez and several other Strikeforce fighters now compete in UFC.
Diaz, the former top UFC lightweight contender, returns to action for the first time since Dec. 8 when he lost by unanimous decision to UFC champion Benson Henderson.
The loss snapped Diaz's three-fight winning streak. He is 16-8 as a pro.