Background The global prevalence of gestational diabetes mellitus (GDM) is increasing, and it can significantly impact women’s psychosocial outcomes in the perinatal period. The aim of this study was to explore the psychosocial impacts including experiences of support for women with GDM in the antenatal and postnatal period. Methods Semi-structured individual interviews were conducted with women (n = 33) living in the UK, who were either pregnant and recently diagnosed with GDM or had a previous GDM diagnosis within the past three years. Interviews were recorded, transcribed, and analysed using reflexive thematic analysis. Findings Analysis revealed six themes: 1. Diagnostic related frustration; 2. Impact on mental health; 3. The medicalisation of eating; 4. Losing agency to gain control; 5. Sourcing networks of support; 6. Current pregnancy; and future reproductive health. Each theme provides a unique insight into the experiences and psychological strain associated with GDM. From confusion and frustration at diagnosis, to the profound knock-on impact a diagnosis, associated lifestyle changes and medical appointments had on women’s mental health, and the perceived medicalisation of their eating behaviours and patterns. Conclusion Given the increasing prevalence of GDM and its wide-ranging psychosocial impacts, this study emphasises the need for healthcare professionals to consider the potential implications of GDM on women’s psychosocial outcome, and to consider alternative support options outside of the medical system, such as peer support.