From 1978 to 1982 he was a chief architect on Business System 12, a database management system that faithfully embraced the principles of the relational model. He works closely with Christopher J. Date and represented IBM at the ISO SQL committees (JTC1 SC32 WG3 Database languages, WG4 SQL/MM) until his retirement from IBM. Darwen is the author of The Askew Wall and co-author of The Third Manifesto, a proposal for serving object-oriented programs with purely relational databases without compromising either side and getting the best of both worlds, arguably even better than with so-called object-oriented databases.
From 2004 to 2013 he lectured on relational databases at the Department of Computer Science, University of Warwick (UK), and from 1989 to 2014 was a tutor and consultant for the Open University (UK) where he was awarded a MUniv honorary degree for academic and scholarly distinction. He was also awarded a DTech (Doctor in Technology) honorary degree by the University of Wolverhampton. He currently teaches a database language designed by Chris Date and himself called Tutorial D.
He has written a book on the card game bridge and has a website on the subject of double dummy problems. Alan Truscott has called him "the world's leading authority" on composed bridge problems.
He was responsible for the double dummy column in Bridge Magazine from 1965 to 1990.