Krayem was one of six people convicted in July of terror murder in the trial of the 2016 Brussels terror attack, in which 32 people were killed.
The sentence was determined in a separate trial, which concluded on Friday.
Krayem has previously been sentenced to 30 years in prison for the 2015 Paris terror attacks, and is likely to serve only 10 years of his life sentence in Belgium.
Osama Krayem was arrested in an apartment in Brussels a couple of weeks after the attacks and has since been detained in Belgium.
Krayem denies participation in the attacks, but admits collusion with the terrorist organization IS.
The text is updated.