The growth in the power of the executive branch of government has been accompanied by a related growth of the importance of executive legal advisors. These advisors can be the first and sometimes only group to review the actions of the executive. In this paper, I compare this practice in four jurisdictions – the UK, Canada, the US and Ireland – to assess its impact on constitutionalism and the executive power. I conclude it can both restrain executive action by holding it within constitutional boundaries; or bolster it by giving legalistic credibility to its actions while providing little restraint in practice. I argue the work of executive legal advisors does not operate as an exogenous constraint but can be structured and manipulated by the executive. As such, I argue that this institution requires much more attention from both comparative constitutional lawyers to map its effects on the constitutional order and to see what structures, processes and cultural factors might shape it.