Dr. William J. P. MacMillan was the eighteenth Premier for the Province of Prince Edward Island since the Province entered Confederation on 1st July 1873. MacMillan was born 24th March 1881, at Clermont, Prince Edward Island, served as Premier for only two years, but was the leader of the Opposition and head of the Island Conservative Party for more than 15 years. The son of Joseph MacMillan, Scottish descent and Mary L. Hogan, Irish descent. First married on 12th January 1909 to Mary B., daughter of Hugh S. MacDonald of South Boston, Massachusetts and they had six children; Dorothea, Bernadette, Joseph, Stephen, Nora and Allan. MacMillan married for the second time on 3rd May 1922 to Letitia Roberts of South Boston. MacMillan resided at 205 Kent Street, Charlottetown, Prince Edward Island.
His youth was marked by an outstanding scholastic record at Prince of Wales College and McGill University where he graduated in 1908 with a degree of Doctor of Medicine. He was the recipient of the Holmes Gold Metal from McGill. He returned to the Island and established a medical practice first in Kinkora and afterwards in Charlottetown in 1910. In 1935, Dr. MacMillan was awarded an honorary Doctor of Laws degree from McGill, one of the few Islanders to be granted this honour.
In 1923, he entered politics, not with a political motive but to try and obtain a grant for his favorite charity, The Red Cross Society. However, he remained in the Legislature after he achieved his first objective and served continuously until 1955 except for the "clean sweep" made by the Liberals during the years 1935 to 1939. In 1932, he was named the first Minister of Health and Education in the province and took over the role of acting Premier during the illness of Premier James D. Stewart. MacMillan was elected as a representative of the Conservative Party in the Charlottetown Common District in the general elections held on 24th July 1923, 25th June 1927 and 6th August 1931. He was reelected in the by-election held on 16th September 1931. He was unsuccessful in the 23rd July 1935 general election and was reelected in the general elections held on 18th May 1939 in the 5th Queens District and was reelected on 15th September 1943, 11th December 1947, 26th April 1951 and was unsuccessful in the general election held on 26th May 1955.
On Stewart's death in 1933, he was named Premier and served until 1935. Dr. MacMillan entered the provincial administration at a time when finances were strained as a result of two fires which destroyed Prince of Wales College and Falconwood, the then Provincial Mental Hospital. He had them both rebuilt and at the same time, elevated Prince of Wales College to Junior College status. Perhaps his greatest success was his procurement of a Carnegie Foundation endowment for the establishing of a Provincial Library System which still serves the Island.
A member of many service clubs, charitable organizations and a member of medical associations, Dr. MacMillan was awarded an O. B. E. for his work during the second World War. He was named a Knight Commander of the Order of St. Gregory the Great in 1947 and installed by Bishop James Boyle in Charlottetown in February 1948. He had been named Lieutenant-Governor of Prince Edward Island on 22nd November 1957, only days before his death on 7th December 1957.