The mother of two from Utah vanished in 2009 and has never been found.
A jury found Steve Powell guilty on all 14 counts. Susan Powell's parents have believed that Steve Powell knows something about their daughter's disappearance. Her father, Chuck Cox, said he hopes the decision will get the family closer to knowing what happened to Susan.
"It kicks another crutch away from him," Cox said. "The main question is: Where is Susan? Now, perhaps he'll answer it."
Authorities have long focused on Susan Powell's husband, Josh Powell, throughout the missing-persons investigation. But Josh Powell killed himself and the couple's two young children earlier this year.
Investigators said Steve Powell has been uncooperative during the investigation.
The voyeurism charges were brought last year after authorities searched Steve Powell's home during their investigation into Susan Powell's disappearance. Investigators said they found thousands of images of females being photographed and videotaped without their knowledge - including Susan Powell.
However, the pictures of Susan Powell were not part of the case. Instead, prosecutors focused on images of two young girls who lived next door to Steve Powell.
The girls, who were about 8 and 10 years old at the time the pictures were taken, were photographed in a bathroom as they bathed and used the toilet. They testified they had no idea someone had taken photos of them in the bathroom.
"He was sitting there, lurking in the shadows, leering at the girls," said Pierce County prosecutor Grant Blinn in court.
The Associated Press contributed to this report.