Bulgaria striker Popov joins Blackburn
The 22-year-old, who scored three goals in 15 matches for Bulgaria, has completed a medical and will complete the paperwork next week subject to obtaining a work permit.
Litex did not disclose the length of the contract.
Popov, scorer of 32 goals in 101 matches in the Bulgarian top flight, was instrumental in helping the Lovech-based club win last season's league title, two national cups and the domestic Supercup.
Bulgarian media reported the deal was worth about 3 million euros although no financial details were provided by Litex.