Blair McClenachan (died May 8, 1812) was a United States Representative from Pennsylvania.
McClenachan was born in Ireland. He immigrated to the United States at an early age and settled in Philadelphia.
He engaged in mercantile pursuits and in banking and shipping, and was one of the founders of and served with the First Troop Philadelphia City Cavalry during the American Revolutionary War. In 1780, he subscribed a large sum of money to help the American forces and aided the Continental Congress with money and credit.
McClenachan was a member of the Pennsylvania House of Representatives from 1790 to 1795, and was elected as a Democratic-Republican to the Fifth Congress, serving from March 4, 1797 to March 3, 1799.
In 1781, his daughter, Deborah, married Colonel Walter Stewart, later Inspector General of the Continental Army and then Major General of the Pennsylvania Militia.
He died in Philadelphia; interment was in a vault in St. Paul's Cemetery.