The bout was announced during the live broadcast of Bellator 116 on Friday.
A former UFC champion, Ortiz (16-11-1) was scheduled to headline the inaugural Bellator pay-per-view in November alongside Quinton Jackson, but was forced off the card due to injury, which pushed the event onto Spike TV.
Ortiz resumed training in February, but the Jackson fight was no longer an option. Jackson (34-11) has entered the Bellator light heavyweight tournament and will face Muhammed Lawal in the final in May.
On Thursday, Shlemenko (50-7) posted an online video stating he would fight Ortiz on the pay-per-view card. The Russian middleweight said moving up in weight class to fight a bigger opponent would be "no problem."
"Tito, I respect you but I must beat you because I am champion," Shlemenko stated. "I know that Tito Ortiz is a light heavyweight. This is no problem for me. I already have fought at light heavyweight. No problem."
Shelemenko, 29, is currently on a 13-fight win streak. His last loss came via decision to current UFC welterweight Hector Lombard in October 2010. He boasts 29 career knockouts.