He is a partner in the Office for Metropolitan Architecture (OMA), and author of the books Four Walls and a Roof: The Complex Nature of a Simple Profession and The Masterplan.

In 2011, De Graaf curated the exhibition On Hold at the British School in Rome about the impact of the financial crisis on OMA's master planning work across the globe.

[4][5] In 2010, De Graaf was involved in the founding of the Strelka Institute for Media, Architecture and Design in Moscow, where he taught topics such as energy planning, the history of utopian predictions and the advent of the megacity.

[6] In 2014, he continued the research on megacities with graduate students at PennDesign, the architecture program at the University of Pennsylvania, under the title Megalopoli(tic)s.[7] In 2018, De Graaf taught a design studio at the Harvard University Graduate School of Design titled “Phantom Urbanism.”[8] The studio produced a database of urban projects that never managed to attract residents.

[9] Since 2018, De Graaf is the Sir Arthur Marshall Visiting Professor of Urban Design in the Department of Architecture at the University of Cambridge.

The Architects' Journal describes The Masterplan as "a short novel about professional vanity, succession within large practices and the Faustian dilemmas facing ‘international starchitects’."