Career
He represented Dufferin in the Legislative Assembly of Ontario from 1919 to 1923 as a United Farmers member and from 1926 to 1934 as a Progressive member. He was born in Melancthon Township, Dufferin County, Ontario, the son of Richard Slack, an immigrant from Ireland, and Elizabeth Silk. Slack served as clerk for Melancthon township.
He later moved to Orangeville.
He died suddenly at the Shelburne District Hospital in 1956 and was buried in Shelburne Cemetery.