Tanner, a Democrat who retired from Congress in 2011 after 22 years in office, will specialize in government relations for Butler, Snow, O'Mara, Stevens & Cannada. Former Mississippi Gov. Haley Barbour has similar responsibilities for the firm in Jackson, Miss., where it is based.
Butler Snow announced the expansion on Thursday, bringing to more than 220 attorneys practicing in 12 offices nationwide.
The firm also has offices in Birmingham and Montgomery, Ala; Jackson, Bay St. Louis, Gulfport and Oxford, Miss.; Nashville and Memphis; Baton Rouge and New Orleans, La.; and Fort Washington and Bethlehem, Penn.
The expansion makes Butler Snow one of the Southeast's largest firms.