In December 1937, influential physician and politician Lord Dawson of Penn introduced an Infanticide Bill into the House of Lords. Seven months later, following minor amendments, Dawson’s Bill passed into law as the Infanticide Act, 1938. This legislation significantly altered the earlier provisions of the Infanticide Act, 1922, which introduced the offence of infanticide into English and Welsh courtrooms for the first time. Under Dawson’s reforms, a woman could be found guilty of infanticide rather than capital murder if the killing of her child, aged no more than one year old, could be attributed to a disturbance in the balance of the mother’s mind following childbirth or from lactation. Although the language and implications of the 1938 Act have ignited significant debate within legal scholarship, the creation of Dawson’s Bill and the leading role medical practitioners played in its enactment have received limited attention from historians. This article helps to address this gap by analyzing the critical response of the inter-war British medical profession to the question of infanticide reform against a backdrop of growing psychiatric ambivalence about a causal link between insanity and female reproductive states. Crucially, this paper contends that ancillary concerns over citizenship, motherhood, and the health of the nation informed Dawson’s motivations and justification for infanticide reform during the 1930s. It also seeks to foreground the physician’s distinct contribution to the birth of the 1938 Act by underscoring his efforts in devising and promoting the Bill within Parliament and among inter-war medical and legal communities.