Shortly after attending Bible School in London, he married a Swedish woman, Ruth.
[1] After eight months in prison, Popov, and other ministers who had been arrested with him, pleaded guilty through a cruel, forced confession.
After moving to the United States in 1970, Popov founded Evangelism to Communist Lands Inc., now known as Door of Hope International to bring Bibles and relief to people in oppressive countries in 1972.
[2] He recorded his testimony and prison experiences in his autobiography Tortured For His Faith: An Epic of Christian Courage and Heroism in Our Day.
In October 1988, during Glasnost, and for the first time in 26 years, Popov was permitted by Bulgarian authorities to visit the church he pastored in Bulgaria.