The Arctic is warming over three times faster than the rest of the planet. This means Arctic ecosystems are changing rapidly, and an important component of these changes are shifts in the amount and distribution vegetation across the biome. Such shifts in vegetation are important because they impact human land use, alter wildlife habitat, and influence how ecosystems function and how this feeds back on the climate. We use field data, along with satellite imagery and machine learning algorithms to map vegetation biomass (i.e. the total mass of living plant matter) across the Arctic. We then use these maps to track changes in plant and woody plant biomass. We found the total amount of Arctic plant biomass increased 14% from 2000 to 2020. Biomass increase was most prevalent in areas with longer growing seasons and more rapid increases in temperature, suggesting climate warming is indeed driving changes in Arctic vegetation. Furthermore, the proportion of biomass attributed to woody plants increased 8% over the same period. This suggests that as the Arctic warms, trees and shrubs are outcompeting non-woody plants. Our findings reveal significant biome-scale changes that have local to global consequences and will likely intensify as climate warming continues.