A veteran US Navy Seal is accused of killing Iraqi civilians at random, stabbing to death a teenage prisoner and nearly a dozen other crimes.
Navy Special Operations Chief Edward Gallagher will plead not guilty when he appears at a hearing at a San Diego naval base, his lawyer said on Friday.
Prosecutors say the highly decorated sniper and medic killed innocent people during his eighth combat deployment.
The 19-year Navy combat veteran faces life in prison if found guilty.
Military investigators allege Chief Gallagher committed several crimes while in Mosul from February to September 2017, including the premeditated murder of a wounded Islamic State (IS) fighter around the age of 15.
He has been held in pre-trial confinement ahead of his criminal hearing, after prosecutors accused him of contacting witnesses.
His wife Andrea Gallagher has called the trial "an atrocity committed against America's service members" and called upon President Donald Trump to intervene.
She, and handful of other supporters wearing "Free Eddie" shirts, cheered the combat veteran as he arrived at the courthouse in handcuffs on Friday.
Aaron Kahn, who said that he is a friend of the accused told CNN that "Eddie's being demonised and not characterised as a good human being".
He added that his service to his country is being "dismissed and not appreciated by the American public and government."
The trial will begin on 19 February.