Sijmons is a landscape architect; he studied architecture and environmental planning at the Technical University of Delft. From 1977 to 1984 he worked at several ministries as a strategic planner. From 1984 to 1990 he was head of the Landscape Architecture Department of the Netherlands State Forestry Service. In 1990 he was one of the three founders of H+N+S Landscape Architects, where he is mainly responsible for research and regional plans. H+N+S received the National Prince Bernard Culture award in 2001. From 1994 to 2010 Sijmons was the chairman of the board of OASE, independent Journal on Architecture Theory. In 2002 he received the Rotterdam-Maaskant award. His book publications in English are Landscape (1998) and Greetings from Europe (2008). His latest book publication is Landscape and Energy (2014) on the implications and design challenges of the energy transition.
Sijmons was appointed first State Landscape Architect of the Netherlands for the period of 2004 to 2008 to advise the Dutch government on landscape matters. He received the prestigious Edgar Doncker Award in 2007. Since 2008 Sijmons has been a professor of Environmental Design at the Technical University in Delft and since 2011 has held the position of chair of Landscape Architecture at the same university. Recently Dirk Sijmons was the curator of the International Architecture Biennale Rotterdam (IABR--2014) with the theme "Urban By Nature." He works on numerous boards, publications and projects as a Senior Advisor to H+N+S Landscape Architects.