In recent decades, historians of English psychiatry have shifted their major concerns away from asylums and psychiatrists in the nineteenth century. This is also seen in the studies of twentieth-century psychiatry where historians have debated the rise of psychology, eugenics and community care. This shift in interest, however, does not indicate that English psychiatrists became passive and unimportant actors in the last century. In fact, they promoted Lunacy Law reform for a less asylum-dependent mode of psychiatry, with a strong emphasis on professional development. This paper illustrates the historical dynamics around the professional development of English psychiatry by employing Andrew Abbott’s concept of professional development. Abbott redefines professional development as arising from both abstraction of professional knowledge and competition regarding professional jurisdiction. A profession, he suggests, develops through continuous re-formation of its occupational structure, mode of practice and political language in competing with other professional and non-professional forces. In early twentieth-century England, psychiatrists promoted professional development by framing political discourse, conducting a daily trade and promoting new legislation to defend their professional jurisdiction. This professional development story began with the Lunacy Act of 1890, which caused a professional crisis in psychiatry and led to inter-professional competition with non-psychiatric medical service providers. To this end, psychiatrists devised a new political rhetoric, ‘early treatment of mental disorder’, in their professional interests and succeeded in enacting the Mental Treatment Act of 1930, which re-instated psychiatrists as masters of English psychiatry.