Ovenden, 70, was convicted in April of six charges of indecency with a child and one count of indecent assault, but he only received 12 months imprisonment suspended for two years at the time.
After Britain's attorney general referred the case to the Court of Appeal, three judges today sentenced Ovenden to two years and three months, as well as rejecting the artist's bid to appeal his conviction.
Paintings and photographs by the artist, often depicting nude girls, have been displayed in galleries all over the world.
"He manipulated them and abused his position of trust," Grieve said.
"The Court of Appeal agrees that the 12-month suspended sentence handed to him was unduly lenient, and I am satisfied they have replaced it with 27 months custody.
"It is right that sexual crimes, whether committed many years ago or more recently, should be punished appropriately. Today the court affirmed this and sent a clear message that people who have behaved in this way in the past will face the consequences through the courts."
The bearded artist had denied the charges, saying they were part of a "witch hunt" in which several high profile people were arrested following the exposure of a child abuse scandal involving late BBC television presenter Jimmy Savile.
Britain's prestigious Tate Gallery removed dozens of Ovenden images from its website after his conviction.
