Born on a farm near Cross Hill, South Carolina, McSwain attended the public schools.

He graduated from Wofford College Fitting School in 1893 and from the University of South Carolina at Columbia in 1897.

He entered the officers' training camp at Fort Oglethorpe, Georgia, May 12, 1917, and served in the First World War as captain of Company A, One Hundred and Fifty-fourth Infantry, until March 6, 1919, when he was honorably discharged.

McSwain was elected as a Democrat to the Sixty-seventh and to the seven succeeding Congresses and served from March 4, 1921, until his death.

He served as chairman of the Committee on Military Affairs (Seventy-second through Seventy-fourth Congresses).