William Irwin was born in Butler County, Ohio, in 1827 and graduated from Marietta College in 1848. He began his career as an instructor at Marietta College before relocating to California, where he engaged in various private industries. Irwin transitioned to public service, being elected to the California State Assembly and later the California State Senate, where he served as President pro tempore. His leadership roles culminated in his election as the 13th governor of California in 1875, serving until 1880.

William Irwin's political career reveals a strategic blend of progressive appointments and fiscal conservatism, exemplified by his appointment of Henry George to a crucial state position. Irwin's governance style demonstrates an intriguing balance between fostering intellectual talent and maintaining a cautious approach to state finances. His tenure as governor was marked by a surprising alignment with reform-minded figures, while his legislative actions suggest a calculated effort to safeguard local economic interests.