Robert Henderson, 73, from Cullivoe, Yell, Shetland, was convicted at the High Court in Aberdeen today.
Henderson had denied seven charges.
The charge that he raped a woman, now in her 60s, twice in 1990 on the island of Yell was found not proven by the jury on a majority verdict.
But he was found guilty of sexual assault charges involving two girls, dating back to the 1970s.
The abuse started when one of the girls was 11.
Detective Sergeant Bruce Peebles said: “Henderson’s offending stretched from the 1970s through to the 1990s when he targeted vulnerable young girls and women within the local community.
“He abused his position as a prominent local businessman, employer and latterly as an elected local councillor to try and disguise his private behaviour with vulnerable girls and women.
“Police Scotland very much acknowledges the courage of the victims who decided to come forward during the enquiry and recognises the lasting effects which Henderson’s actions have had on them throughout their lives. It is also acknowledged that his actions and the subsequent enquiry have had a very large impact on many people on the island of Yell, where the crimes took place, and in the wider Shetland community, not least upon the members of Henderson’s own immediate family and where a sufficiency of evidence exists, such crimes will be reported for consideration of prosecution in court.
“I would take this opportunity to encourage anyone who has been a victim of such crimes in the past that should they wish to report this to the police, they will be treated sensitively, listened to, and all such allegations will be investigated thoroughly.”
Henderson will return to court in May for sentencing.