Rhodes entered the British Army in 1838, and served in Canada East, from 1842 to 1844.In 1847, he retired from the army as a captain and settled in Sillery, Canada East.
During the same year, he married Anne Catherine Dunn, granddaughter of Thomas Dunn and Mathew Bell, at the Cathedral of the Holy Trinity in Quebec City, on 16 June.
The following year, Rhodes purchased Sillery's Benmore Estate (French: domaine Benmore), which has been designated a component of the Sillery Heritage Site since 1964.Rhodes was one of the founders of the Union Bank of Lower Canada.
He was president of the Quebec Bridge Company, the North Shore Railway, the Quebec and Trois-Pistoles Railway, and the Quebec and Richmond Railway.
Rhodes was also president of the Quebec Geographical Society, a justice of the peace, and a lieutenant in the militia.
He served in the Quebec cabinet as Commissioner of Agriculture and Colonization.
Rhodes was defeated when he ran for reelection in 1890.
William Rhodes died at his residence of the Benmore Estate in Sillery, at the age of 70.