A decorated Navy SEAL plans to plead not guilty Friday to murder in connection with the fatal stabbing of a 15-year-old ISIS prisoner and other war crimes, his attorney said.

Special Operations Chief Edward Gallagher is expected to attend an arraignment hearing at Naval Base San Diego, according to Phil Stackhouse, who said his client was being falsely accused by disgruntled SEALs who disliked the platoon leader.

Gallagher, who was twice awarded the Bronze Star, was portrayed by Navy prosecutors as an elite warrior and medic who went off the rails during his eighth deployment – killing the captured jihadist, who was estimated to be 15 years old, and then posing with his body.

If convicted, the 19-year veteran faces life in the slammer.

During a preliminary hearing in November, investigators said Gallagher stabbed the teen after he was handed over to the SEALs in the Iraqi city of Mosul to be treated for wounds sustained during an airstrike in May 2017.

A naval investigator told the court that a SEAL medic told him he believed he had just stabilized the teen when Gallagher “walked up without saying anything at all” and started stabbing him.

He later took photos of himself with the corpse, holding up his knife in one hand and the boy’s head in the other, prosecutors said. He also posed with the body during his re-enlistment ceremony, the official said.

When another SEAL questioned Gallagher, the chief replied that “I was working on him, and he just died,” said Joe Warpinski, a Naval Criminal Investigative Service agent.

Gallagher also is accused of shooting an elderly man carrying a water container in Mosul in June 2017, and a month later shooting a girl in the same area.

Investigators told the court that Gallagher had threatened to publicly name fellow SEALs if they reported his actions.

Some fellow warriors were so concerned about his actions that they did not tell him his sniper rifle settings were off so his shooting would be less accurate and they would fire warning shots to scatter civilians, Warpinski said.

Prosecutors also have accused Gallagher’s platoon commander, Lt. Jacob Portier, of not acting on the allegations. His attorney Jeremiah Sullivan said Portier was the first to report them to superiors and did so as soon as he learned of them.

Stackhouse plans to ask the judge to allow Gallagher to be released from the brig, where he has been held since his Sept. 11 arrest.

“He’s never run from a fight, and he’s not going to run from this one,” he said.

With Post wires