Eirik Jensen, who was responsible for combating organised crime in the capital Oslo, was arrested in 2014.
On Monday, a court found he had received at least 667,800 kroner (€71,300, £63,200) in bribes to help smuggle tonnes of hashish into Norway.
He denies the charges and plans to appeal, his lawyer said.
Jensen's 21-year sentence for corruption was the maximum permitted under the law, and a rare event in Norway.