Conventional identification of leukemia based on visual inspection of blood smears through a microscope is time-consuming, error-prone, and is limited by the hematologist’s physical acuity. Therefore, an automated optical image processing system is required to support clinical decision-making. To address this problem, we developed a machine learning-based real-time automated diagnostic system to assist medical care workers. Blood smear slides (n = 250) were prepared from clinical samples, imaged, and analyzed in Jimma Medical Center, Hematology department. The system was able to categorize four common types of leukemia’s through a robust image segmentation protocol, followed by classification using the support vector machine. It was able to classify leukemia types with an accuracy, sensitivity, and specificity of 97.69%, 97.86% and 100%, respectively for the test datasets, and 97.5%, 98.55% and 100%, respectively, for the validation datasets. The computer-assisted diagnosis system took less than one minute for processing and assigning the leukemia types, compared to an average period of 30 minutes by unassisted manual approaches. Moreover, the automated system complements the healthcare workers’ in their efforts, by improving the accuracy rates in diagnosis from ∼70% to over 97%. Importantly, our module is designed to assist the healthcare facilities in the rural areas of sub-Saharan Africa, equipped with fewer experienced medical experts, especially in screening patients for blood associated diseases including leukemia.