Marcel Proust, 1913-27. Seven volumes, ~1.3M words. Memory, time, society — the longest psychological novel ever written.
From Wikipedia
In Search of Lost Time, first translated into English as Remembrance of Things Past, and sometimes referred to in French as La Recherche, is a novel in seven volumes by French author Marcel Proust. This early twentieth-century work is his most prominent, known for both its length and its theme of involuntary memory.