Rea joined Kawasaki in 2015 after six season at Honda in WSBK, with the Ulsterman going on to dominate the series aboard the ZX-10RR.
He won six consecutive championships between 2015 and 2020, setting the record for the most race victories in the process at 119.
Rea was dethroned by Razgatlioglu aboard the Yamaha in 2021, while Ducati dominator Alvaro Bautista was champion last year and is well on course to do the same again in 2023.
The 37-year-old Northern Irish rider has a Kawasaki deal in place for 2024, though the competitiveness of the ZX-10RR has waned in recent years, with Rea only so far winning once in 2023.
One of the big shocks of the 2024 rider market came earlier this year when Razgatlioglu announced he would be leaving Yamaha to join BMW, also ending faint hopes of a MotoGP switch with the marque next season.
With Razgatlioglu's departure to BMW, Rea has seen the possibility of having access to a more competitive bike right now and after nine seasons at Kawasaki with the same team, he has decided that it is time to take his chances in WSBK as he nears the end of his career.
Source: Autosport