In December, an Oslo appeals court upheld a guilty verdict against Kendrick Wallace, but cleared three other former executives in the case: two Norwegians, including former CEO Thorleif Enger, and a Frenchman.
Wallace's sentence, which the lower court had set at two-and-a-half years, was extended because the appeals court found he had played a "central" role in the bribery payments.
In addition, "as senior legal advisor he occupied a central position in the company's anti-corruption work", the court ruled.
In what the Norwegian media has dubbed "the biggest corruption scandal in Norwegian history", the partly state owned Yara paid a record 295 million kroner (€32.4 million, $38.5 million) fine in January 2014 for lining the pockets of top Libyan and Indian officials in order to win contracts.
The Libyan part of the case involves the payment of at least $5 million in bribes to the son of Libya's ex-oil minister serving under dictator Moamer Kadhafi, Shukri Ghanem, in connection with the construction of a fertiliser plant in Libya together with the National Oil Corporation (NOC) and the Libyan Investment Authority (LIA).
Ghanem was found dead in April 2012 in the Danube river in Vienna, where he was in exile after the fall of the Kadhafi regime. An investigation concluded that the 69-year-old Libyan had suffered a heart attack.