Gestational diabetes mellitus (GDM) is a common medical condition during pregnancy and is linked to short- and long-term complications for both mothers and offspring. However, there is limited information regarding poor glycaemic control in Malaysia. This study aims to determine the predictors of poor glycaemic control among women with GDM and to explore women’s perceptions and experiences in self-managing glycaemic control. An explanatory sequential mixed methods study was conducted among women with GDM in Northern Terengganu. A proportional-to-size stratified sampling method was used in quantitative research to obtain 238 samples. Logistic regression was applied to determine associations between factors and poor glycaemic control. Then, purposive sampling was done in qualitative inquiry to obtain 12 samples. Thematic analysis was applied to identify recurring themes. The data from both quantitative and qualitative inquiry were then combined to answer research questions. Dietetic counselling (AOR = 2.95; 95% CI: 1.41, 6.17; p-value=0.004) and diet self-efficacy (AOR = 0.78; 95% CI: 0.61, 0.98; p-value=0.040) were associated with poor glycaemic control. Six themes that emerged from the interviews were: fear and worry; knowledge and motivation; dietary preferences and beliefs; family factors; occupational factors; and availability and affordability. The findings provide useful evidence for healthcare providers in delivering comprehensive health education and providing care for women with GDM.