The Süper Lig outfit also revealed that they have a future buy-out clause option to sign Omeruo on a permanent deal until next summer.
Omeruo was snapped up by Chelsea in January 2012 and spent last season on loan at Championship side Middlesbrough.
The 21-year-old defender was part of the Middlesbrough team that ensured promotion to the Premier League last season.
“I’ve come to Turkey to reciprocate the club’s determination to bring me here. I want to show the manager and the fans that they have made a good choice and I am completely focused on breaking into the squad and prove myself here.
“They have strong faith in my ability and I need to prove it. Last season was difficult because of injuries which affected me both at club and international level but I have put all that behind me.
“Kasimpasa approached Chelsea in a professional manner and the chance to test myself in a top league is very challenging.”
Omeruo passed his medical on Tuesday before putting pen-to-paper on his new deal.
The Nigerian international defender has represented the Super Eagles at U-17, U-20 and senior level. The young defender was part of the Nigeria team that reached the Last 16 of the 2014 World Cup.