The prevalence of common mental diseases, including schizophrenia, generalized anxiety disorder, generalized depression, and other related disorders, is high in emerging nations. We have developed a diagnosis and suggestion model based on ontologies to improve services and assist both individuals and psychiatrists. Our application of Semantic Web Technology was to generate domain-based knowledge. Information for domain ontology-based knowledge development was gathered from domain experts and other expert-written publications. This ontology model’s concepts, relationships, and attributes can be applied to the diagnosis and recommendation of common mental illnesses. Using valid links between ontology concepts, the SWRL rules are built to identify the type of mental condition based on the symptoms in the domain ontology. Our investigation was carried out using the Design Science research methodology. Using Protégé Editor, we expressed the acquired knowledge as an ontology-based architecture, and we used Pellet Reasoner to assess the coherence of the domain ontology we had constructed. We can search the domain ontology for solutions, drugs, advice, and other pertinent data.