In the wake of COVID-19, higher education institutions worldwide were forced to continue teaching and learning through online means. However, it was only during the pandemic that institutions in Uganda, such as Kabale University, embraced online learning. Against this background, one could not predict how students drastically adapted to the new normal, especially in mathematics, which requires a lot of practice. Thus, this study sought to establish the relationship between behavioural intention to use technology and the adoption of online mathematics learning among pre-service teachers at Kabale University. We conceptualized behavioural intention to use technology according to the Unified Theory of Acceptance and Use of Technology (UTAUT) as comprising four factors: performance expectancy, effort expectancy, facilitating conditions, and social influence. This mixed methods study followed a cross-sectional correlational survey and hermeneutic phenomenological research designs. We collected data from 140 pre-service mathematics teachers, who were sampled using stratified and simple random sampling techniques, through a self-administered questionnaire. Also, we collected qualitative data through nine face-to-face interviews of pre-service mathematics teachers using criterion sampling, where the most prominent criterion was the participant's experience with the phenomenon under study. Using Pearson’s linear correlation, results showed that all UTAUT constructs were related to the adoption of online learning. Simple linear regression revealed that facilitating conditions were the strongest predictor. Furthermore, the narrative analysis indicated that, among others, a lack of technological knowledge hindered learners’ effective participation in online mathematics lectures. Therefore they barely benefited from online learning. Thus, we recommend government universities enhance teachers’ and learners’ technological knowledge, among other facilitating conditions such as establishing strong on-campus Wi-Fi connections as online learning continues.