The paucity of skilled manpower in sub-Saharan Africa limits the delivery of effective interventions for the mentally ill. Individuals with mental disorders and their caregivers frequently consult clergy when mental symptoms cause distress. There is an urgent need for collaboration with nonprofessionals in order to improve mental health care delivery and close the widening treatment gap. Using a cross-sectional descriptive method, we explored clergy’s (Christian and Muslim) aetiological attributions for common mental illness (schizophrenia and depression) from Benin City, Nigeria, as well as their willingness to collaborate with mainstream mental health services. We observed that a majority of clergy surveyed were able to correctly identify mental illnesses depicted in vignettes, embraced a multifactorial model of disease causation, and expressed willingness to collaborate with mental health care workers to deliver care. Clergy with a longer duration of formal education, prior mental health training, and Catholic/Protestant denomination expressed a greater willingness to collaborate. Educational interventions are urgently required to facilitate this partnership.