The Dallas Medical Examiner says Loncar was found in his car in the parking lot of his office.
His cause of death has not yet been determined.
Loncar's 16-year-old daughter died earlier in the month.
Brian Loncar's advertisement's were known as being entertaining and noticeable for years across Texas. Loncar's phrase "The Strong Arm" branded him as one of the most recognizable attorneys in the area.
Loncar's firm was based in Dallas, but his firm handled cases across the state.
This is a developing story. Stay with ABC13 for the latest.