Purpose We assessed the association of total meat, processed, and unprocessed red meat and iron intake with the risk of developing gestational diabetes mellitus (GDM) in pregnant women. Methods We conducted a prospective study among 3298 disease-free Spanish women participants of the SUN cohort who reported at least one pregnancy between December 1999 and March 2012. Meat consumption and iron intake were assessed at baseline through a validated, 136-item semi-quantitative, food frequency questionnaire. We categorized total, red, and processed meat consumption and iron intake into quartiles. Logistic regression models were used to adjust for potential confounders. Results We identified 172 incident cases of GDM. In the fully adjusted analysis, total meat consumption was significantly associated with a higher risk of GDM [OR = 1.67 (95% CI 1.06-2.63, p-trend 0.010)] for the highest versus the lowest quartile of consumption. The observed associations were particularly strong for red meat consumption [OR = 2.37 (95% CI 1.49-3.78, p-trend < 0.001)] and processed meat consumption [OR = 2.01 (95% CI 1.26-3.21, p-trend 0.003)]. Heme iron intake was also directly associated with GDM [OR = 2.21 (95% CI 1.37-3.58, p-trend 0.003)], although the association was attenuated and lost its statistical significance when we adjusted for red meat consumption [OR = 1.57 (95% CI 0.91-2.70, p-trend 0.213)]. No association was observed for non-heme and total iron intake, including supplements. Conclusions Our overall findings suggest that higher pre-pregnancy consumption of total meat, especially red and processed meat, and heme iron intake, are significantly associated with an increased GDM risk in a Mediterranean cohort of university graduates.