Ivanov, 21, is a regular with Bulgarian youth national teams and has made one cap with the senior side. He scored four goals while starting all 10 matches in qualification for the U-21 European Championship.
He broke into Levski's first team at 16 for his debut and made 85 appearances with the club, adding 13 goals and 15 assists. He has played all across the front line, including both wings and center forward.
"As we continue to build a strong and competitive roster for 2021 and beyond, it was important that we added another talented, young attacking player," sporting director Georg Heitz said in a club statement. "Stanislav is a dynamic and hard-working winger who fits our style of play extremely well. We expect him to be an integral part of the team moving forward."
Ivanov is Chicago's third acquisition of the offseason, following Nigerian forward Chinonso Offor and Ecuadorian defender Jhon Espinoza. All three players are 21 or younger.