The fight takes place at Revel Casino in Atlantic City, N.J.
Shamhalaev replaces Bellator Season 6 Featherweight Tournament winner Daniel Straus, who was forced to withdraw from the bout after fracturing his left hand during a recent training session.
"When Daniel went down with his injury, I reached out to Shahbulat and his manager to see if he was ready for this fight, and without hesitation his answer was 'Yes,' " Bellator chairman and CEO Bjorn Rebney said. "After watching Shahbulat's run through our last tournament, I couldn't think of a better fight to end our season than Curran-Shabulat on April 4."
Shamhalaev (12-1-1) won the Season 7 145-pound tournament on Feb. 21, when he knocked out Rad Martinez in the second round at Bellator 90.
Curran (18-4) makes his second defense of the title he won in March 2012 with a third-round knockout of Joe Warren.
In his most recent outing on Jan. 17, Curran retained his belt with a split decision over Patricio Freire.