The Republic of Korea was looking for a new aircraft to replace the outdated F-4E Phantom II and F-5E/F Tiger II aircraft in its national inventory. During this process, in parallel with the development of the aviation industry, the country opted to build an aircraft using national resources instead of buying one already built. KAI (Korea Aerospace Industries) had previously developed the KT-1 and T-50 trainer aircraft, then produced the FA-50 aircraft (Advanced Jet Trainers & Light Combat Aircraft), and managed to export them to various countries, and established close ties with Lockheed Martin for the F-16 production and T-50 development projects. This close relationship would be their greatest asset during the design, development, and production of the KF-21.

The next-generation fighter aircraft KF-X project was started by the Republic of Korea in 2010. For the Project's EMD (Engineering, Manufacturing, and Development) Program, businesses were chosen, and agreements were made in 2015. PDR (Preliminary Design Review) and CDR (Critical Design Review) were completed in 2018 and 2019, respectively. The roll-out ceremony of the prototype took place on April 9, 2021.