Trade unions face long-term challenges including declining memberships that threaten their influence. COVID-19 created new challenges and possibilities for renewal. This article presents findings from a study conducted during the pandemic, comprising a large survey and interviews that investigated how unions adapted to the changes to working life they and their members faced. Evidence from UK unions shows unions rapidly changing how they worked, particularly in adopting and investing in new technologies. COVID-19 became a trigger for adaptation for unions which helped to meet the challenges created by the pandemic and demonstrated unions' creative ability to adapt and maintain relevance. The article contributes new insights about union renewal and argues that renewal should be understood as a continuous and evolving process of adaptation and transition, shaped as much by internal strategy as external shocks. It argues that confidence within unions about their ability to reform is important for understanding renewal.