This article explores how differences in prime ministers’ leadership styles may affect parliamentary influence in security policy. Drawing on work on personality differences in political psychology, I argue leadership style is a critical but often overlooked factor in the growing area of research on parliaments and foreign affairs. My key argument is that prime ministers vary in how they respond to and manage parliamentary involvement in security policymaking. I propose Leadership Trait Analysis to capture prime ministers’ orientations towards parliamentary involvement. I examine the plausibility of my argument with intra-country comparisons of Turkish and UK prime ministers’ orientations towards parliament in specific cases of security policy. More generally, this article challenges more formal-institutional approaches to parliaments’ role in security policy. A focus on prime ministers has an analytic advantage of bringing together some of the various factors (such as intraparty divisions and public opinion) to explain parliamentary influence in security policy.