The use of systems thinking (ST) to handle complexity and wicked policy problems is gaining traction in government and the Civil Service, but policy makers and civil servants can encounter several challenges in practice. How best to support them in understanding and applying ST in policy making is not well understood. This study aims to explore civil servant and expert perspectives on the drivers and values of ST and the challenges, successes and solutions for its adoption in policy making. We conducted semi-structured interviews with 31 civil servants across 17 UK government departments, agencies and public bodies, and 5 experts skilled in supporting ST use in policy making. Via thematic analysis, we identified the values, challenges and successes interviewees experienced when implementing ST and their definitions of the term systems thinking. Civil servants were drawn into an ST approach by their academic training and exposure to it in their previous role(s), workshops, networking events and apprenticeships and through appreciating its values. Civil servants provided various interpretations of ST concepts and values with a strong emphasis on ‘complexity’ and ‘interrelationship’. Our analysis identified eight challenge themes for the implementation of ST in policy making, including (i) ST language and interpretation, (ii) the policy landscape, (iii) government structure and operation, (iv) methodology and technical aspects, (v) capacity and expertise, (vi) conceptualisation, expectations and buy-in, (vii) stakeholders, engagement and collaboration and (viii) evaluation and evidence. Despite the high interest in ST among civil servants across different policy areas within the UK government and the Civil Service, implementation is challenging. Recommendations for implementation include ST language in policy, systems leadership, policy-specific capacity development and evaluation processes for collecting evidence of impacts.