Dr Haasnoot is an environmental scientist specialized in water management, climate adaptation, integrated assessment modeling and decision-making under deep uncertainty. She developed the Dynamic Adaptive Policy Pathways (DAPP) method to support decision making uncertain change. Recent work focuses on adaptation to sea level rise in deltas and monitoring for signal detection to implement or adjust adaptive plans. She designed and led the research on impacts of accelerated sea level rise in the Netherlands, which triggered the national Research Program on Sea Level Rise of the government to assess the dutch adaptation strategy. The thread in Dr Haasnoots work is on assessing societal impacts of climate change, sea level rise, socio-economic developments and alternative management options to develop robust and adaptive plans, which she worked on in various countries worldwide, including USA, New Zealand, UK, Bangladesh, Indonesia, Thailand, Viet Nam, Croatia, Cyprus, Romania, Russia.

Dr Haasnoot is also affiliated to Deltares where she leads the strategic research program on climate adaptation at Deltares. She is a lead author for Sixth Assessment Report of the UN Intergovernmental Panel on Climate Change (IPCC) (Working Group II, chapter Europe and crosschapter cities and settlements by the sea).

In March 2023, Marjolijn was appointed a member of the Scientific Climate Council of the Netherlands. This advisory body provides the government with solicited and unsolicited advice on climate policy.