Provided is a method for manufacturing a ball joint including a ball-seat molding step for forming a ball seat assembly by using, as a core, a ball section of a ball stud, the ball section of which is integrally provided in advance at one end portion of a stud section, and insert-molding a ball seat made of resin to cover at least a portion of the ball section present on an opposite side to the stud section, and a housing molding step for insert-molding a housing made of resin by using, as a core, the ball section partially covered by the ball seat of the ball seat assembly.