Investigators said off-duty Officer Rodney Thomas, 52, was involved in an accident on the bridge at about 1 a.m. and had stepped out of his personal vehicle to check on the other driver when he was struck.
Thomas was taken to the hospital, where he died.
Investigators are looking for a white 2011 or 2012 Porsche Panamera that fled eastbound toward Slidell after striking the officer. It is not known if the car has local or out-of-state plates.
According to witnesses, the Porsche was driving erratically before it struck Thomas.
Thomas had been with the New Orleans Police Department since March 2005. He had spent his entire career with the department in the Second District. He leaves behind a wife and two children.