Tacoma police spokesman Mark Fulghum said the suspected shooter has been arrested, but investigators are still trying sort out exactly what prompted the attack.
"Now it's just a matter of sorting out what happened," he said.
Police were called to the scene in the 6200 block of McKinley Avenue East just after 1 a.m., and officers found one of the victims dead in a rear passenger seat of the car.
The other person who had been shot was taken to a hospital but their condition was not known.
Fulghum said the victims were in the car with three other people when they were shot.
The name of the person who was killed has not been released.