Oscar Dana Allen was born on February 24 or 25, 1836, in Hebron, Maine.

In 1871, he received a PhD. in chemistry from Yale University and became a professor of analytical chemistry and metallurgy at the Sheffield Scientific School of Yale University from 1871 to 1887. His professional research was done chiefly on cesium and rubidium with the results published in the American Journal of Science. He also edited and revised the American edition of Fresenius' “Quantitative Analysis” in 1881. He was an amateur botanist interested in the study of bryology and corresponding with prominent bryologists and botanists of North America. He collected many species of mosses and hepatics and two of them were named in his honour, Thuidium allenii and Fontinalis allenii. In 1884, he moved to California and later to Washington, where he collected many western flowering plants for the Gray Herbarium of the Harvard University. With his son John A. Allen, he assembled the moss herbarium that was later purchased by the New York Botanical Garden. He was also a linguist interested in the study of obscure languages.

In 1861, he married Fidelia Totman. He died on February 19, 1913, in Ashford, Washington.