He attended secondary school at Wesley College, Auckland.
A teacher by profession, he was an Member of Parliament from 1981 to 1996, representing the National Party. He was first elected to Parliament in the 1981 election as Member of Parliament for Taupo, defeating the incumbent Labour Member of Parliament, Jack Ridley. He became Minister of Youth Affairs and Associate Minister of Education and Social Welfare during the Third National Government.
He later held the role of Commissioner for Children.
McClay was the chairman for Keep New Zealand Beautiful until July 2009. He has been involved in a number of other charities, including the New Zealand Spinal Trust, World Vision, Heart Children New Zealand, Variety, the Children"s Charity and Foreign the Sake of Children.
In March 2010 he was charged with misuse of taxpayer-subsidised flights. In August the same year he pleaded guilty.
He repaid the two charities that he had defrauded, Keep New Zealand Beautiful and World Vision.
He was convicted and given a sentence of 300 hours of community work.In addition he was stripped of his travel benefits by the Parliamentary Services Commission.