I am doing research work on the writings of William Faulkner and thinking of adding a Faulkner novel to my course on Law and Literature (probably Requiem for a Nun)
I recommend Philip Weinstein's Becoming Faulkner: The Art and Life of William Faulkner. Philip Weinstein has done strong, focused work on modernism (see his Unknowing: The Work of Modernist Fiction) and Faulkner especially. His twin brother, Arnold, has written widely and creatively on modernism, too.
I have two candidates: William Faulkner: His Life and Work, by David Minter ( The Johns Hopkins University Press) and, more recent, Faulkner: A Biography, by Joseph Blotner ( University Press of Mississippi)
I wrote my PdD dissertativo on a comparative study between William Faulkner and the Brazilian Graciliano Ramos. The best biography on Faulkner that I used was Stephen B Oates: William Faulkner: The Man and the Artist, A Biography. If you are looking for a biographical study of the author for literary criticism study, this is a great pick. It helped me a lot on Faulkner's literary creative craft and his statement that all his work derived from a postcard of his native town, and his concept of reality, observation and imagination. Good luck!