Inmate Latu Kepu has been sentenced to six years and four months jail for the manslaughter of Waikato prison guard Jason Palmer.

Kepu, 22, was sentenced in the High Court at Hamilton today after earlier pleading guilty to the manslaughter of Mr Palmer, 33, a former United States Marine, at Spring Hill Prison on May 15.

He was the first prison guard killed on active duty.

Kepu is currently serving two years, eight months for similar violent offences including attack against a police officer and a pregnant woman.

In court today Justice Paul Heath described Kepu's actions as "cowardly".