His research was part of the United Nations Intergovernmental Panel on Climate Change that shared the 2007 Nobel Peace Prize with Al Gore.

[4] In 1998 he was appointed to the National Oceanic and Atmospheric Administration (NOAA) Science Advisory Board; in 1999 he was elected by the Woods Hole Oceanographic Institution (WHOI) Board of Trustees as a member of the corporation for a three-year term; in 2000 he was appointed a member of the Advanced Scientific Computing Advisory Committee by the U.S. Secretary of Energy; and in February 2009 he was elected to the National Academy of Engineering (NAE) "for pioneering the development of coupled climate models, their use on parallel supercomputing architectures, and their interpretation.

[6] Washington received the U.S. Department of Energy's Biological and Environmental Research Program Exceptional Service Award for Atmospheric Science in 1997, for the development and application of advanced coupled atmospheric-ocean general circulation models (GCMs) to study the impacts of human activities on future climate.

In January 2000 Washington was given the Charles Anderson Award from the American Meteorological Society (AMS) for pioneering efforts as a mentor and passionate supporter of individuals, educational programs, and outreach initiatives designed to foster a diverse population of atmospheric scientists.

[2][7][8] In 2019, Washington and Michael E. Mann were awarded the Tyler Prize for Environmental Achievement, recognized as the top honor in environment-related work.

He is a fellow of the American Philosophical Society (APS), and he has received honorary doctorates from Oregon State University and Bates College.