Arc. Onajide is the Managing Partner/Director of A.T.Onajide Architects Ltd. He holds a a Bachelor of Arts (Hons) in architecture from the Manchester Polytechnic (now Manchester Metropolitan University), a Diploma with Honours in Architecture and a Post Graduate Certificate in Professional Architectural Studies from Thames Polytechnic (now University of Greenwich).
He served as Chairman of Western Projects Consortium Ltd (WPC Ltd), a multidisciplinary company that was involved with the zonal project management of the Petroleum (Special) Trust Fund. He is an active member of the Nigerian Institute of Architects and is a member of various professional associations.