Marcus Wade Madison, 42, was accused of shooting the deputy and initiating a 17-hour standoff with police last Wednesday and Thursday in Big Lake.
Madison is said to have surrendered to police after the standoff and was found with a self-inflicted gunshot wound to the face.
Media reports state that the preliminary cause of Madison's death was the gunshot wound, but officials earlier stated that they believed the injury was not life threatening.
Deputy Josh Mitchell was killed August 1 in the line of duty.
Madison was a resident of Lake Brownwood and had confrontations with Brown County law enforcement in the past, according to Brown County Sheriff's reports.