Kessler was employed by P. J. Berkman as a designer at the Fruitland Nursery in Augusta, Georgia when he was engaged by Robert Jemison Jr to prepare landscape plans for the Mountain Terrace subdivision of Birmingham. After the completion of that project he remained in the city helping Jemison plan and develop the Redmont, Forest Park, and Central Park neighborhoods. He also worked on a plan for Woodrow Wilson Park, for the planned industrial city of Fairfield, and for the suburb of Mountain Brook. Kessler was the designer of the picturesque "Old Mill" on Shades Creek, of the landscaping at the Mountain Brook Club, Mountain Brook Elementary School, and of the Memorial Garden at the Birmingham Museum of Art. He also worked with Warren & Knight architect on the design for several new buildings on the campus of the University of the South in Sewanee, Tennessee in 1920.
Kessler constructed his William Kessler residence at 1437 18th Street South in 1913. He was the founder of the Birmingham Horticulture Society in 1914. He kept offices on the 16th floor of the Empire Building in the 1920s.