Before he became a writer, he practised law. His philosophy was influenced by Herbert Spencer, particularly Spencer's views on evolution. In books such as Outlines of Cosmic Philosophy (ISBN 0384157807), Fiske aimed to reconcile science and orthodox religious beliefs. Fiske was a popular lecturer on these topics in his early career and later turned to historical writings instead, publishing books such as The Discovery of America (1892, ISBN 1932080422).