Background: Mental capacity legislation in the UK is designed to safeguard the rights of people who may need support, or may be unable, to make autonomous decisions. Very limited evidence has been published about the impact of the COVID-19 pandemic on the application of mental capacity legislation and, to our knowledge, none on the ability of speech and language therapists (SLTs) to support people with communication disabilities to engage in decision-making. Aims: To describe how UK SLTs supported people with communication disabilities to make decisions and participate in mental capacity assessments, best interests decision-making and advance care planning during the COVID-19 pandemic. Methods & Procedures: This descriptive, cross-sectional study used an online survey to collect quantitative and qualitative data about SLTs' practice experiences between August and November 2020. SLTs working with a range of adult clinical populations in different care settings were sampled purposively from all UK jurisdictions. Participants were recruited through professional networks and social media. Quantitative data were summarized using descriptive statistics. Qualitative data were analysed thematically. Outcomes & Results: Data were collected from 107 SLTs working in a range of settings across all four UK nations. The sample included SLTs working with people with neurological conditions, learning disabilities, mental health conditions and acute confusion. The need for SLT support appeared to increase during the pandemic. Most respondents were still able to offer support; however, the amount and nature of support varied. Quality of support was impacted by adjustments associated with social distancing and infection control restrictions. Personal protective equipment (PPE) was identified as a barrier to communication. Indirect working methods (e.g., telehealth) were inaccessible to some people with communication disabilities. Most respondents felt confident that legal requirements were upheld, but suggested this group was less able to engage in decision-making and had reduced access to support to manage their own health conditions. Conclusions & Implications: Some SLT services were limited in their ability to meet the decision-making support needs of people with communication disabilities during the COVID-19 pandemic due to structural and systemic barriers. This suggests that existing inequities in the provision of care for people with communication disabilities in the UK were amplified during the pandemic.