Born Paisley, Scotland; apprenticed as a jeweller; in 1850 purchased land in Iowa to establish a cooperative (though Gardner never lived there); 1851 owner and editor of newspaper Glasgow Sentinel; 1856 moved to America and began running photographer Matthew Brady's Washington DC gallery; worked for Brady 1856 to 1862, photographing the American Civil War; opened own gallery in Washington DC with his brother James in 1863; 1866 published 'Gardner's Photographic Sketch Book of The American Civil War'; photographed Native Americans and surveyed the proposed route of the Kansas Pacific Railroad, many of his photographs stereoscopic; after 1871 gave up photography and founded an insurance company.