Okoli will return to the ring on May 24 in Rzeszów, Poland. The former world featherweight champion will fight local reigning world bantamweight champion Lukasz Różański.
"We will remember how to knock out opponents," Gallagher said on social media on the occasion.
In Poland, Okolie will have a chance to win the world title in his second weight class. Różański will be making his first defense of the World Boxing Council 101.6kg title he won last year.