After graduating from Transylvania University in 1828, Clay gained an appointment to the U.S. Military Academy at West Point.

Their son, Thomas Clay McDowell, was a major figure in Thoroughbred horse racing in Kentucky.

After starting his law career, in 1835 Clay was elected as a member of the Kentucky State House of Representatives, serving a two-year term to 1837.

On January 1, 1847, he wrote a letter back to his Kentucky family: "John asks me to give his Xmas compliments to you.

"[2] Clay was killed in action while leading a charge of his regiment in the Battle of Buena Vista on February 23, 1847.