Father Gainor was born in Greencastle, Indiana, on April 30, 1885. He received his early education in St. Lawrence parochial school in Muncie, Indiana, but after a year or two in the high school department of Notre Dame University he discontinued his studies and went to work, first in the steel mills, and then for the telephone company in Muncie, and also in Philadelphia.

While employed in Philadelphia he attended high school in night sessions at Temple University and completed his studies at Aquinas College, Columbus, Ohio, in preparation for entering the Order. He received the habit at St. Joseph's Priory, Somerset, Ohio, in 1919, and there made profession in August 16, 1920. After a year's study of philosophy in St. Rose Priory, Springfield, Kentucky, he was sent to the Dominican House of Studies, Washington, D.C., where, having also matriculated at the Catholic University of America, he was ordained in St. Dominic's Church, June 4, 1926.

He was first assigned to teach at Providence College, but when Fenwick High School opened in Oak Park, Illinois, in the Fall of 1929, he served for six years as Principal of the school and as superior of the community of his brethren. Upon the expiration of his term of office, he was appointed pastor and superior of St. Dominic's, Youngstown, Ohio, in which capacity he served for three years. He then became successively Dean of Studies at Aquinas College, Columbus, Ohio, Prefect of Discipline at Fenwick High School, Subprior at Holy Rosary, Minneapolis, Minn., Chaplain for the Dominican Sisters, Sinsinawa, Wisconsin, assistant in the parish at St. Dominic's, Denver, Colorado, and finally assistant at St. Pius, Chicago, where, aside from his parish duties, he devoted himself to writing for which he had a predilection from his student days and eminent talents, though previously he had had little leisure for such endeavors. He died quite suddenly on April 18, 1967 and was buried in the Dominican plot in All Saints Cemetery, Des Plaines, Illinois.