This study aimed to assess the knowledge, attitude, and practices (KAP) of patients with type 2 diabetes mellitus (T2DM) in Jeddah, Saudi Arabia. A cross-sectional study was conducted among 307 participants from four diabetes clinics in Jeddah. A validated Arabic questionnaire was used to assess participants’ KAP scores, which were then analyzed against demographic characteristics. The study participants had a mean age of 44 ± 6.9 years, with a higher proportion of women (52.8%) than men (47.2%). Almost half of the sample (45.9%) held university degrees, whereas only 1.6% were illiterate. The mean knowledge score was 10.03 ± 3.45, with women scoring marginally higher than males (10.15 ± 3.37 vs. 9.90 ± 3.54). Similarly, the mean attitude score was 56.16 ± 12.85, with women scoring higher (56.94 ± 12.97) compared to males (55.38 ± 12.73). However, male patients outperformed female patients in practice scores (11.28 ± 3.82 vs. 10.99 ± 3.69). Logistic regression analysis revealed significant associations between higher KAP scores and advanced education, longer duration since diabetes diagnosis, and having relatives with diabetes (P < 0.05). Additionally, single, widowed, and divorced participants had significantly lower attitude scores (P < 0.05). In addition, age and income levels also showed significant correlations with KAP scores (P < 0.05). Education level, age, disease duration, income, family history of diabetes, and marital status significantly influenced the KAP scores of patients with. These findings highlight the need for tailored diabetes education programs to enhance patients’ KAP and improve health outcomes.