LONDON—A British arms dealer who helped ship thousands of assault rifles and millions of rounds of ammunition from China to Nigeria has been sentenced to seven years in jail.

Gary Hyde was convicted on two counts of breaching U.K. trade controls and concealing criminal property for moving the weapons without a license and hiding more than 620,000 pounds ($1 million) in commission payments.

While the 2006 deal between the Chinese and Nigerian governments was lawful, Hyde failed to get a license for his part in it—something Judge Nicholas Loraine-Smith chalked up to greed.

Sentencing Hyde at London's Southwark Crown Court on Wednesday, Smith said it would have been easy for him to apply for a license. He called Hyde's offenses a "sustained and deceitful flouting of the law."