1988, the Canadian Governor General's Conservation Award; and, in 1992, he was awarded the Governor General's Canada Medal for "distinguished service to Canada." In the autumn of 1990, McMillan was Distinguished Lecturer, Distinguished Lecturer Series, International Institute for Protected Areas Management, at the Universities of both Alberta and Calgary. In June 2019, at its annual Gala Awards Dinner, Corporate Knights ("The Company for Clean Capitalism," which represents Fortune 500-type companies committed to sustainable development) bestowed on McMillan its Award of Distinction for his pivotal role in the Montreal Protocol. After leaving the Environment portfolio, he remained active in international, national, and local issues alike, including built heritage preservation. When in 1981 an historic bank building in his riding was demolished, there was an outcry from concerned citizens, among them McMillan. He summed up the loss of this historic structure, "The actions of the Canadian Imperial Bank of Commerce in Charlottetown have been decidedly more imperial than Canadian." He became increasingly active in such preservation causes in Prince Edward Island. These included the restoration of a unique pre-Confederation brick powder magazine—located in Brighton Compound in Charlottetown—the demolition of which the Canadian Army had begun until McMillan led a public campaign to stop it. McMillan remained Environment minister until he was defeated in the 1988 general election due to opposition to the Canada–United States Free Trade Agreement among his constituents. In August 1989, McMillan was appointed Canada's consul-general to Boston. The first person ever appointed from Atlantic Canada as Canadian Consul General to New England, at Boston, McMillan was awarded an honorary doctorate by Bridgewater State University in 1993 for—in the words of its president, Dr. Adrian Tinsley -- "significant accomplishment on behalf of Canada in support of strong, enduring Canadian-American cooperation and ties." He maintained his involvement in politics, and attempted unsuccessfully to regain his seat in the 1993 general election. At the urging of the new Progressive Conservative Party leader, Jean Charest, a close friend and former Mulroney government Cabinet colleague, McMillan reluctantly attempted another comeback, this time in the 1997 general election, in the riding of Peterborough, Ontario. But he was defeated by Liberal candidate Peter Adams and (very narrowly) by the Reform Party's Nancy Branscombe. Prior to entering electoral politics, in the late 1970s, McMillan was, successively, Policy Secretary to Rt. Hon. Robert L. Stanfield, Leader of the Official Opposition in the Canadian House of Commons; an executive