Background English NHS guidance emphasizes the importance of involving users in commissioning cancer services. There has been considerable previous research on involving users in service improvement, but not on involvement in commissioning cancer services. Objective To identify how users were involved as local cancer service commissioning projects sought to implement good practice and what has been learned. Design Participatory evaluation with four qualitative case studies based on semi‐structured interviews with project stakeholders, observation and documentary analysis. Users were involved in every stage from design to analysis and reporting. Setting and participants Four English cancer network user involvement in commissioning projects, with 22 stakeholders interviewed. Results Thematic analysis identified nine themes: initial involvement, preparation for the role, ability to exercise voice, consistency and continuity, where decisions are made, closing the feedback loop, assessing impact, value of experience and diversity. Discussion Our findings on the impact of user involvement in commissioning cancer services are consistent with other findings on user involvement in service improvement, but highlight the specific issues for involvement in commissioning. Key points include the different perspectives users and professionals may have on the impact of user involvement in commissioning, the time necessary for meaningful involvement, the importance of involving users from the beginning and the value of senior management and PPI facilitator support and training. Conclusions Users can play an important role in commissioning cancer services, but their ability to do so is contingent on resources being available to support them.