The woman, who is now 51, confronted the man about the assaults in 2010 and told him the abuse stopped her from having any long-term relationships and children.
She went to police a year later claiming the assaults started when she was just 12, three years before her mother married the man in 1976. The mother died in 1995.
The man, identified only by the initials G.M., admitted he had sex with the woman when they lived together in West Vancouver, but claimed the sex started when she was 19 and was consensual.
B.C. Supreme Court Justice Gregory Fitch acquitted the man on the first count of having sex with a female under the age of 14, saying he wasn't satisfied with the woman's timeline that she was 12 when the first assault happened.
However, Fitch found the man guilty on the remaining two counts from when she was between the ages of 14 and 16, ruling the man knew she didn't consent to his sexual advances.