In December 1917, Woolf became one of the co-founders of the 1917 Club, which met in Gerrard Street, Soho.
As his wife's mental health worsened, Woolf devoted much of his time to caring for her (he himself suffered from depression). In 1917, the Woolfs bought a small hand-operated printing press and with it they founded the Hogarth Press. Their first project was a pamphlet, hand-printed and bound by themselves. Within ten years the Press had become a full-scale publishing house, issuing Virginia's novels, Leonard's tracts and, among other works, the first edition of T. S. Eliot's The Waste Land. Woolf continued as the main director of the Press until his death. His wife suffered from severe bouts of mental illness throughout her life, until her suicide by drowning in 1941. Later, Leonard fell in love with a married artist, Trekkie Parsons.
Among his nine siblings, Bella Woolf was also an author. His brother Cecil Nathan Sidney Woolf was the author of Poems (published 1918); Cecil was killed in World War I in 1917. His dissertation Bartolus of Sassoferrato, his Position in the History of Medieval Political Thought was expanded to a book published by Cambridge University Press in 1913 in collaboration with his brother Philip. Philip and Cecil also translated Stendhal's On Love (Duckworth, 1915).