Born on a farm near Lloyds, Virginia, Whitelaw moved with his father to Cape Girardeau County, Missouri, in 1856.
He attended private schools in Tappahannock and Staunton, Virginia, and the law department of the University of Michigan at Ann Arbor.
He was admitted to the bar in 1873 and commenced practice in Cape Girardeau, Missouri.
Whitelaw was elected as a Democrat to the Fifty-first Congress to fill the vacancy caused by the death of James Peter Walker and served from November 4, 1890, to March 3, 1891.
He retired from active law practice in 1927 and moved to Blodgett, Missouri, and in 1934 to Blytheville, Arkansas, where he died on July 27, 1937.