Merricks has been awarded the honour for services to the financial services industry.
Money Management editor Janet Walford was also given a CBE for services to journalism and the financial services industry.
Merricks joined the FOS as chief ombudsman in 1999 when it was created and before that was the insurance ombudsman at the Insurance Ombudsman Bureau, joining in 1996.
He began his law career in 1972 as founding director of the Camden Law Centre, aimed at helping local residents get legal aid, before becoming a lecturer in law at Brunel University in 1976.
He then joined the Law Society as assistant secretary general in 1985.
FOS spokeswoman Emma Parker says: “Walter has committed a large portion of his professional life to the development of ombudsman schemes – both at the Insurance Ombudsman Bureau and at the Financial Ombudsman Service and through his involvement with the British and Irish Ombudsman Association. This award is a tribute to the commitment he has shown in making ombudsman schemes an effective way of resolving disputes and making justice accessible for consumers.”