It was unclear how Pluto's demotion might affect the mission of NASA's New Horizons spacecraft, which earlier this year began a 9 1/2-year journey to the oddball object to unearth more of its secrets.
The decision at a conference of 2,500 astronomers from 75 countries was a dramatic shift from just a week ago, when the group's leaders floated a proposal that would have reaffirmed Pluto's planetary status and made planets of its largest moon and two other objects.
That plan proved highly unpopular, splitting astronomers into factions and triggering days of sometimes combative debate that led to Pluto's undoing.
Now, two of the objects that at one point were cruising toward possible full-fledged planethood will join Pluto as dwarfs: the asteroid Ceres, which was a planet in the 1800s before it got demoted, and 2003 UB313, an icy object slightly larger than Pluto whose discoverer, Michael Brown of the California Institute of Technology in Pasadena has nicknamed Xena.
Charon, the largest of Pluto's three moons, is no longer under consideration for any special designation.
