Objectives: To develop a core outcome set (COS) to capture and measure the well-being of doctors working in the NHS. Design: An online Delphi study. Setting: United Kingdom National Health Service. Participants: Participants from four stakeholder groups: i) those who might use the COS in research, ii) organisations that measure/capture NHS staff wellbeing, iii) professionals with experience managing NHS staff wellbeing, and iv) NHS doctors, were identified through authorship of relevant publications, attendee lists of doctor well-being conferences and meetings, professional bodies, participation in a previous study and recommendations from others. They were recruited via email. Method: A two-stage process: 1) creating a list of 43 wellbeing outcomes informed by a systematic review of wellbeing measurement instruments, a survey of UK doctors and 2 doctor engagement workshops, and 2) an online modified Delphi study (with two rounds) to reach consensus. Outcomes were rated on a 9-point Likert scale; consensus was reached when ≤75% agreed that an outcome was critical for inclusion in the COS. Results: Fifty-two participants completed both Delphi rounds. Seven wellbeing outcomes met the threshold for inclusion in the COS: General wellbeing, Health, Personal safety, Job satisfaction, Morale, Life work balance, and Good clinical practice. Conclusion: Use of the COS has the potential to reduce heterogeneity and standardise the capture and measurement of doctor well-being and ensure outcomes important to all stakeholders are reported. Trial registration: This study was prospectively registered with the COMET initiative www.comet-initiative.org (Registration: 1577)