He was educated at Rugby School and Christ's College, Cambridge,[1] and later became a banker at Grant and Maddison's Union Banking Company in Southampton.

[2] The Darwins had no children of their own, and after his wife died, William devoted himself much to his nieces Gwen Raverat, Frances Cornford, and Margaret Keynes.

Raverat remembered him fondly as an eccentric and entirely unselfconscious man in her childhood memoirs Period Piece (1952).

He was sitting in the front seat as eldest son and chief mourner, and he felt a draught on his already bald head; so he put his black gloves to balance on the top of his skull, and sat like that all through the service with the eyes of the nation upon him.William is primarily notable as a subject of Charles Darwin's studies of infant psychology.

[2] Charles Darwin published his findings in the journal Mind in June 1877, in an article titled "A biographical sketch of an infant".