National Human Rights Institutions (NHRIs) have a crucial role in promoting constitutionalism and human rights. The modern NHRIs can be traced from South Africa's transformative project, as part of bodies meant to support the societal transformation and ingrain constitutionalism. Their structure, objectives, and functions differ from the traditional human rights institutions since they have a constitutional entrenchment of their independence, enormous powers, the obligation of other state organs to assist them, the prohibition on their interference, and their obligation to report to the National Assembly. These designs and functions are meant to support their role as constitutional watchdogs. The Kenya and Zimbabwe Constitutions have transplanted NHRIs to support their transformative constitutional projects. This research assesses the ability of these institutions to promote constitutionalism. First, it addresses the structural and operational design of the NHRIs. Second, it conducts a functional analysis of these institutions. Third, it considers the practical challenges in promoting constitutionalism. Fourth, it discusses how the challenges are being overcome. The paper argues that NHRIs are remarkable in promoting constitutionalism. However, they must take a proactive approach such as being engaged in the budgeting process. Also, the NHRIs should walk the fine line between cooperating with other government institutions and maintaining independence. Overall, the paper concludes that the protection of NHRIs should go beyond legal text to practice through, for example, fixing their minimum funding in law.