This method for manufacturing a ball joint (J) includes: a ball seat molding step in which a ball part (10b) of a ball stud (10), to which the ball part (10b) is integrally provided in advance at one end of a stud part (10s), is used as a core, and a plastic ball seat (12) is insert-molded so as to cover at least a portion of the ball part (10b) on the opposite side from the stud part (10s), whereby a ball seat assembly (12A) is formed; and a housing molding step in which the ball part (10b), a part of which is covered by the ball seat (12) of the ball seat assembly (12A), is used as a core, and a plastic housing (11) is insert-molded.