He was born in Scarborough Township, Canada West, the son of James W. McCowan, an immigrant from Scotland.
He resigned his seat in the provincial assembly in 1913 and was appointed sheriff for York County, serving until 1934.
In 1891, he married Georgina Ashbridge, from a pioneer family, residing in the eastern end of the growing city of Toronto.
In the 1905 Ontario general election, McCowan defeated a new Liberal candidate, Walter Scott, as incumbent and former Scarborough Township Reeve John Richardson (Ontario MPP) had resigned prior to the Election to become York County Court Clerk.
Meanwhile, McCowan and 25 other Conservative MPP's became the governing party under Premier Sir James P. Whitney.