Oscar E. Denniston was born in Kingston, Jamaica, and was educated in that city. Early in life he became drawn to mission work and was associated with a seaman's mission in Kingston. He was a large man, and his physical strength was necessary in the work which he had to do, for he was called upon to safeguard his flock physically as well as spiritually.
In 1902 Rev. Denniston was asked to become the pastor of the small struggling Baptist Church in Oak Bluffs, Massachusetts. The chaplain of the local seafarer’s mission had met Rev. Denniston previously and felt that Rev. Denniston had the skills to lead the church.
It was under his care and pastorate that the struggling church grew to become an important Island institution. Rev. Denniston obtained an old motion picture theater and succeeded in converting it into a church structure. His congregation increased, particularly in summer, when packed auditoriums have been the rule.
For forty years Rev. Denniston continued his work in this parish, never drawing a cent of guaranteed salary, yet, as he often smilingly said—"always receiving everything necessary for his comfort and wellbeing". However, that may be, the side of his life that he kept chiefly to himself would have revealed many sacrifices for the good of others. His great heart was filled with pity for those who were in need, and he did not shrink from going without himself, that he might provide something for those less fortunate. His home lacked many conveniences, because he felt that he could do without them and in this manner he might have more to bestow on others.
Year round, he walked the streets, calling on his parishioners and doing whatever he could to make life brighter for them. His standing among the Island clergy, regardless of faith, was enviable; everyone admired and trusted Rev. Denniston. "A Christian gentleman," was the characterization given by one of the priests of the Roman Catholic parish, and this opinion was widely shared. "A mighty factor on the side of law and order," once said a police officer. Always keenly awake to civic duties and activities which might affect the public as a whole, Rev. Denniston never missed a town meeting or similar gathering, nor did he hesitate to speak his mind.
About 1933, Rev. Denniston suffered a serious illness from which he never fully recovered. He hoped for a return of his strength and ability to work. He felt that his task was incomplete. Certain objectives which he had set for himself and his church had not been gained and he dreaded to think of leaving this work unfinished. He had continued to work as he wished, but his failing strength had long been apparent to those who knew him best and only his iron-will kept him active. He died March 3, 1942 and is buried in Oak Grove Cemetery, Oak Bluffs, Massachusetts.