Background Treatments for long-term control of asthma have improved and include a promising but expensive class of biologic therapies. However, the clinical trials evaluating these and other novel treatments have used a variety of different outcomes to evaluate efficacy. The evolution of asthma care calls for a re-examination of outcomes that are most important to patients and other stakeholders. Objective To develop a core set of outcomes to be measured in phase 3 and phase 4 clinical drug trials in patients with moderate-to-severe asthma. Methods We used a robust and in-depth multistakeholder consensus process bringing together patients, clinicians, regulators, payers, health technology assessors, researchers, and product developers to reach consensus on outcomes. We used a modified Delphi method to reach consensus, an approach adapted from the Core Outcome Measures in Effectiveness Trials Initiative aligned with contemporary methodological standards for core outcome set development. Results The following outcomes were included in the final core set: severe asthma exacerbation, change in asthma control, asthma-specific or severe asthma-specific quality of life, asthma-specific hospital stay (ie, >24-hour stays at any level of care) or admission, and asthma-specific emergency department visit. Conclusion These 5 outcomes represent a minimum set of core outcomes for use in phase 3 and phase 4 clinical drug trials in moderate-to-severe asthma. Consistent collection of these outcomes as minimum, independent of whether additional heterogeneous primary or secondary outcomes are included, will allow for meaningful comparisons of the effect of asthma therapies across clinical trials.