Shri GP Thareja graduated with degree of M.Sc. (Chem.) in 1965 and with a degree of LL.B. in 1967. After graduation, he taught chemistry to post-graduate students and procedural laws to undergraduates, at affiliated institutes of University of Kanpur.

He served as a judicial officer in Delhi for 32 years before superannuation in 2004, in which time period he adjudicated upon several matters including Priyadarshini Mattoo murder case and Naina Sahni muder case. As a judicial officer, he was appointed by Hon'ble Supreme Court of India to enquire into matter of hawkers & squatters etc., in area of New Delhi Municipal Corporation. While serving as a judicial officer, he obtained LL.M. degree from the University of Delhi, in 1979. Also, he presented papers at the 'World Congress on Law & Medicine' organised by the Indian Law Institute, New Delhi in 1985 and the Seminar on 'Criminal Justice in India - Problems & Perspectives' organised by the Law Commission of India in 1994. He was also invited as guest faculty to teach administrative law at Indian Law Institute, New Delhi (now called Indian Law Institute (Deemed University), New Delhi.

Post retirement, he has donned the robes of an Advocate and appeared in several cases including Arushi Talwar murder case, CP Shootout case & Uphaar Tragedy case. Also, the Hon'ble High Court of Delhi appointed him as an amicus curiae in several matters and assigned him judicial work, including enquiry in relation to illegal appointments in Hardyal Municipal Public Library, Delhi. He is also on the panel of arbitrators at Delhi International Arbitration Centre and is often invited by the Delhi Judicial Academy as a resource person on procedural laws.