Background: Adherence to treatment is crucial for achieving effective glycaemic control and preventing complications in Type 2 Diabetes Mellitus (T2DM). However, poor adherence to pharmacological and non-pharmacological interventions remains a significant barrier worldwide. Objectives: This study aimed to assess the prevalence of treatment non-adherence among patients with T2DM, identify socio-demographic and clinical factors influencing adherence, and examine its impact on glycaemic control. Methods: A cross-sectional study was conducted at a secondary care hospital in King Koti, Hyderabad, from March to August 2025. One hundred patients with T2DM were randomly recruited. Data were collected via structured questionnaires assessing sociodemographic information, treatment adherence (pharmacological and lifestyle), glycaemic monitoring practices, comorbidities, and barriers to adherence. Descriptive statistics were used for analysis. Results: The mean age of the participants was 54.66 years for males and 53.69 years for females. A majority (93%) resided in urban areas. Obesity was prevalent in 91% of participants, higher among females (53%) than males (38%). Hypertension was the most common comorbidity (45%). Pharmacological adherence was better, with 63% on dual therapy; however, 15% reported medication non-adherence, which was more common in females (11%). Non-pharmacological adherence was poor, with only 53% following dietary recommendations and a mere 15% engaging in regular exercise. HbA1c testing was performed in 34%, mostly showing abnormal values. Forgetfulness, lack of awareness, and neglect of lifestyle modifications were the principal reasons for non-adherence. Conclusion: Non-adherence to treatment, especially lifestyle modification, remains a critical barrier to effective glycaemic control in T2DM. Along with general physician, pharmacist-led personalized counselling and structured education programs are recommended to improve adherence and diabetes outcomes in secondary care settings. In summary, the study findings validate and extend previous research emphasizing that medication adherence alone is insufficient to achieve optimal glycaemic control without concurrent lifestyle adherence and adequate monitoring. Addressing these multifactorial barriers requires a holistic, multidisciplinary, and patient-centered approach to diabetes management.