State officials say the ruling means more than 100 people face resentencing for crimes including robbery, murder, kidnapping and sexual abuse.
In deciding the appeal of Andre Jerome Lyle Jr. on Friday, the court said required minimum sentences for juveniles are unconstitutional because they amount to cruel and unusual punishment. Lyle was 17 years old in 2010 when he was convicted of robbery and sentenced to up to 10 years in prison.
Three justices disagreed with the Iowa ruling. It follows a U.S. Supreme Court decision last year that all no-parole juvenile lifers must be considered for parole.