McGowan was the son of Irish immigrants.
McGowan trained as a lawyer and served for thirteen years as a member of the South Carolina House of Representatives. His civil career was interrupted by the Mexican War. In 1846 he entered the Palmetto Regiment and rose to the rank of Captain, Staff.
He became a Brigadier in the Army of Northern Virginia, in the army of the Confederacy. Orr's Regiment, with which JW's brother, William McN. Whistler served, was in McGowan's brigade in the Wilderness campaign during the American Civil War.
At the close of the war, McGowan returned to Abbeville and was a member of the state convention of 1865 and elected to Congress that year, only to be denied a seat by the Republican majority. He was a leader against the carpetbaggers and was again elected to the State Legislature in 1878, and in 1879 was elected an Associate Justice of the South Carolina Supreme Court, a post he held until 1893.
http://www.aztecclub.com/bios/mcgowan.htm (accessed 2004).