Warren has been with Harkness Henry since 1970 and became a partner in 1972. He is a past president of the District Law Society and has chaired the Law Society’s Standards (disciplinary) Committee and also the Complaints, High Court Practice and Ethics committees.
Warren’s specialist areas are now litigation relating to wills, trusts and estates but, in the past, he has acted for successful plaintiffs on some of the leading New Zealand cases about professional negligence. He has also enjoyed success in the criminal courts where he defended, doctors, lawyers, accountants and senior police officers on serious criminal charges. He has achieved ‘not guilty’ verdicts in several high profile criminal cases.
In 2014 the University of Waikato awarded Warren an honorary doctorate in recognition of his contributions to the University’s School of Law and the legal profession in the Waikato.