Warner was born in Suffield, Connecticut. As a young man he worked as an artisan and a telegraph operator. In 1869 he had saved up enough money to move to Paris, where he studied sculpture at the Ecole des Beaux-Arts under Francois Jouffroy, and worked as an assistant for Jean-Baptiste Carpeaux.
When the French Third Republic was proclaimed in 1870, he enlisted in the Foreign Legion, resuming his studies when the siege was over (May 1871). In 1872 he removed to New York and established a studio. He was one of the founders and a member of the Society of American Artists in 1877, and an associate of the National Academy of Design in 1888.
After meeting with little commercial success, however, he returned to live at his father’s farm in Vermont, where he also did work for manufacturers of silver and plated ware. Towards the end of his life his sculptures became known to a wider audience.
He died in 1896, after a cycling accident in New York's Central Park. In the 1970's Warner's heirs donated Olin Levi Warner's collection of personal papers to the Smithsonian Archives of American Art.
Warner is credited for having brought the French Beaux Arts style to the United States, and popularizing the bas relief through numerous portraits in this style. Among his best known works are:
Warner’s great-grand uncle was the Revolutionary leader Seth Warner.