(1) Background: Type 2 diabetes mellitus (T2DM) is a global disease with a compelling impact on developed and developing economies across the globe. The World Health Organization (WHO) (2020) reported a global prevalence of 8.5% in 2014 among adults aged at least 18 years. Consequently, the condition led to a 5% increase in premature mortality from 2000 to 2016. Aim: The scoping review sought to examine illness perception and medication adherence among adult patients with T2DM. (2) Methods: The study was conducted in 2021 and covered articles published in English in the last five years. PubMed, MEDLINE, CINAHL, and ScienceDirect were the primary search engines used to generate the required scholarly records. A total of 20 studies met the inclusion criteria. (3) Results: The 20 studies selected for the scoping review covered different themes on the overall concept of illness perception and medication adherence in adults with Type 2 Diabetes Mellitus. Each study presented unique implications for research and influence on the policymaking relating to the treatment or the management of type 2 diabetes mellitus in adults of different aged groups. (4) Conclusions: The studies reveal both high and low adherence to medications in adults with type 2 diabetes mellitus. The management and treatment of the condition depend on the uptake of oral hypoglycemic agents or insulin as well as the recommended therapies to enhance the clinical outcomes of the patients.