The implementation of radiation therapy advanced practice in Australia has not yet been broadly realised. With anticipated growing demands on cancer services, it is imperative to understand why this is the case, and to strategise a way forward. As a result, we explored the factors influencing the implementation of advanced practitioner radiation therapists (APRT) in Australia. The research outcome was a complex process of Navigating Uncertainty, which described the contextual, social and personal factors surrounding implementation successes and challenges. Further synthesis of the findings was undertaken to highlight the fundamental features influencing this process, with the intention to provide a useful understanding for practitioners seeking APRT implementation. Data were collected through national online focus groups and case studies with 53 participants. Analysis identified a constructivist grounded theory process of Navigating Uncertainty. Further analysis of the categories and properties of the process was undertaken to synthesise findings at a higher level of abstraction. Four overarching and intertwined factors were influencing the implementation of APRT. Uncertainty occurred when practitioners attempted to conceptualise and assimilate the new role into the workplace. Power was apparent in the advocacy and legitimisation of the APRT by centre leaders. Value was vital to achieving purposeful outcomes. Identity was evident in the personal transition of the APRT, and in the boundary work with others. Recognising and negotiating uncertainty, power, value and identity is essential for APRT implementation strategies to succeed. A framework to guide practitioners towards the implementation of APRT has been described that embodies these factors.