The COVID-19 pandemic has resulted in significant alterations to and implications for the lives of millions of people, and especially for those with pre-existing medical conditions. The aim of this study was to explore the lived experience of older people with type 2 diabetes mellitus (T2DM) throughout the first 9 months of the pandemic, with emphasis on the habits of physical exercise. We conducted a qualitative study using semi-structured interviews. The data consist of telephone interviews of seventeen older people with T2DM (10 women and 7 men, aged 62–76 years). Using thematic analysis, five themes were generated: (1) an altered social and relational life; (2) changes in routine and attitude regarding physical activity behaviour; (3) home-related activities gained relevance; (4) health and well-being impact and management; and (5) thoughts about the post-pandemic period. The increase in the number of cases and the fear of becoming infected with COVID-19 limited the social (i.e., contact with family and/or friends) and functional (i.e., daily routine, the habit of exercising) lives of these people, reverberating negatively on their health and well-being. Feelings of isolation, loneliness, anxiety were common. The findings of this study help to better understand the impact of the pandemic and determine areas of need for future interventions. A multidisciplinary approach is necessary to provide support for older people with T2DM and tackle the negative effect of the pandemic, including the reduction in physical activity.