Rajan is a specialist surgeon with expertise in surgery of the head, face and neck. Rajan obtained his medical degree (MBChB) from the University of Glasgow in 1995; he was awarded MRCS from the Royal College of Surgeons in 1998 following basic surgical training and FRCS from the Royal College of Surgeons in 2005 following advanced surgical training in otorhinolaryngology, head and neck surgery (ORL-HNS).

Thereafter, Rajan spent 3 years of further fellowship sub-specialist training in head and neck surgery and reconstructive surgery of the head and neck at the Royal Prince Alfred Hospital, University of Sydney (1 year), and at the Toronto General Hospital, University of Toronto (2 years). In recognition of his expertise in head and neck surgery, Rajan was appointed Consultant Surgeon at Auckland City Hospital in 2009.

Rajan also has a strong background in research. He has published over 40 articles in scientific journals as well as several book chapters on head and neck surgery. In 2005 he was awarded Doctor of Medicine (MD) diploma by the University of Glasgow for his research efforts, and in 2010 he was appointed Honorary Senior Lecturer at the University of Auckland. Rajan regularly lectures and teaches surgery overseas.

Rajan is a member of the Australian and New Zealand Head and Neck Society, the American Head and Neck Society, the New Zealand Society of Otolaryngology Head and Neck Surgery, the British Association of Otorhinolaryngologists, Head and Neck Surgeons, the British Association of Head and Neck Oncologists.