John Barr (March 4, 1843 – November 19, 1909) was an Ontario-based Canadian physician and political figure.

He represented Dufferin in the Legislative Assembly of Ontario from 1875 to 1879, from 1890 to 1894 and from 1898 to 1904 and in the House of Commons of Canada from 1904 to 1909 as a Conservative member.

He was born near Elizabethtown (later Brockville) in Canada West in 1843, the son of Irish immigrants.

He was Deputy Master in the South Grey County Orange Lodge.

Barr first set up practice in Horning's Mills but later moved to Shelburne.