William Barber (March 1808 – August 26, 1887) was a Canadian businessman and politician.
His family came to Canada from County Antrim in Ulster, Ireland in 1822. The four Barber brothers built a woollen mill, foundry and sawmill in Georgetown, Ontario. In 1854, they built a paper mill on the Credit River near Streetsville, Ontario. In 1888, his nephew, John Roaf Barber, upgraded the mill to use hydroelectricity power, one of the early industrial applications of electricity in Canada.
In 1862, Barber built a brick home near Streetsville, Ontario now known as The Old Barber House.
He was a member of the Legislative Assembly of Ontario for Halton from 1867 to 1875. In 1871 the Liberal Party dropped Barber as their candidate in the upcoming election, due to his support for Premier J. Sandfield Macdonald's self-described "Patent Combination" government. In his stead, the party selected William Durie Lyon and the radical 'Clear Grits' platform he championed. Despite the withdrawal of Liberal support, Barber ran as an independent and successfully fended off Lyon's challenge, largely thanks to the significant Conservative support he had acquired.
Following the 1871 election however, Lyon provided a crucial vote to his former Liberal peers when they moved to oust Sandfield Macdonald's ministry, and supported the subsequent Liberal government. He was again adopted as the Liberal Party candidate at the 1875 election and won reelection as such. The victory was shortlived however. Following the 1875 election, he was unseated for having induced a voter to stay home, and did not stand in the subsequent byelection held on November 15, 1875. He was succeeded by which was won by his erstwhile Liberal rival Lyon.