Bellator 123 will take place at Mohegan Sun Arena and air on Spike TV.
Curran (20-5) reclaimed the Bellator featherweight title in March with a submission victory over Daniel Straus in the fifth round. The 26-year-old champion first won the belt in March 2012 and defended it twice before losing it to Straus in November 2013.
In his first title defense, Curran narrowly defeated Freire (21-2) via split decision at Bellator 85 in January 2013.
Freire punched his ticket back into title contention by winning the Bellator Season 9 featherweight tournament in November.
Nicknamed the Pitbull, Freire hasn't lost since dropping the decision to Curran. He will carry a four-fight win streak, which includes three knockout finishes, into the title fight.
In addition to the main event, Bellator announced a light heavyweight bout between Muhammed Lawal (12-4) and Tom DeBlass (9-2). Also on the card, heavyweight Bobby Lashley (10-2) will make his promotional debut opposite Josh Burns (8-7).