Martin Cannermo, 26, denied involvement, but the Attunda district court said it was unanimous.
The regalia, a gold funeral crown and an orb made for King Charles IX (1550 to 1611), and a crystal-studded gold crown made for Charles’ second wife, Kristina the Elder were stolen on July 31.
Witnesses said they saw two men flee by bicycle from the Strangnas Cathedral, west of Stockholm, and then by motorboat on nearby Lake Malaren.
Cannermo has been in pre-trial detention since February, when another man, Nicklas Backstrom, was sentenced to four years and six months for his role in the theft.
The court said it reduced Cannermo’s sentence for aggravated theft since he had contributed to the recovery of the stolen items, and was recently sentenced for another theft.
The main evidence cited in the ruling was that DNA from Cannermo was found on the king’s crown and orb, which were recovered in February.
The regalia were found in a trash container placed on the roof of a car in Akersberga, North of Stockholm.
Cannermo claimed he received them from an unnamed person and placed them there.
Backstrom, 22, initially denied the charges during his trial, although traces of his blood were found in the cathedral after the unexpected find of the stolen items.
He later admitted to the theft.