Smith was born in Georgetown, Kentucky, and was a brother-in-law of Horace Randal and a distant relative of John Bell Hood.

On May 31, 1862, because he was the senior major general in the Army of Northern Virginia, Smith briefly took command after Gen. Joseph E. Johnston was wounded at Seven Pines.

However, Smith's nerve broke, and Jefferson Davis replaced him with Robert E. Lee the following day, June 1.

[2] In late August, Smith returned and took command of the defenses around Richmond, which was expanded to become the Department of North Carolina & Southern Virginia in September.

Smith was also the superintendent of the Etowah Iron Works from 1863 until June 1, 1864, when he was commissioned a major general in the Georgia Militia, commanding its first division until the war's end.

Smith died in New York City in 1896 and was buried in the Cedar Grove Cemetery in New London, Connecticut.