The 28-year-old told the club's website: "I'm happy to be back at West Brom. Last season I was a little bit late for pre-season because I was waiting for the deal to happen.
"This year it's good for me that I will be here for pre-season. This time I will start with the group and I'll be ready like everybody else.
"It is always good when you have competition. Liam [Ridgewell] is a good player and a good guy. I have a lot of respect for him. Everybody has to fight for their own place in the team. Last year I didn't play a lot of games and this year I hope to play more. I know the league now and I'm not afraid of anyone."
Popov made 12 appearances for the Baggies last season.