Background: Women are twice as likely to experience depression compared with men. Midlife is a period of increased vulnerability to depression in women and is a stage that coincides with the menopausal transition. Although prospective studies suggest that depressive symptoms increase during this period, findings are inconsistent and it remains difficult to disentangle the effects of reproductive aging from chronological aging. We examined trajectories of depressive symptoms across midlife in relation to reproductive and chronological aging and assessed the association between menopause stages and depression. Methods: We analysed data from 2,036 women from a UK community-based pregnancy cohort followed over three decades from the early 1990s to early 2020s. Depressive symptoms were assessed at up to 11 timepoints using the Edinburgh Postnatal Depression Scale (EPDS), with depression defined as a score [≥] 13. Linear mixed effects models were used to characterise trajectories of depressive symptoms across reproductive and chronological age, and to estimate associations between menopause stages and depression, adjusting for ethnicity, social class, age at menarche, educational attainment, material hardship, social support, smoking status, body mass index (BMI), and alcohol intake. Results: Depressive symptoms increased gradually with both reproductive and chronological age; however, there was little evidence of a marked increase in levels of depressive symptoms during the peri- or postmenopause stages. Compared with the reproductive period, perimenopause was associated with higher odds of depression (OR 1.19; 95% CI 1.03 to 1.39), whereas there was no evidence of increased odds during postmenopause (OR 0.99; 95% CI 0.83 to 1.19). Conclusions: Overall, reproductive ageing appears to contribute relatively little to long-term changes in depressive symptoms beyond the broader effects of chronological ageing. The odds of depression were highest in the perimenopause and did not persist into postmenopause, indicating that this stage may represent a window of vulnerability for a subgroup of women. Identifying such subgroups could help inform targeted prevention and support strategies.