Abstract Biomass from short‐rotation coppice (SRC) of woody perennials is being increasingly used as a bioenergy source to replace fossil fuels, but accurate assessments of the long‐term greenhouse gas (GHG) balance of SRC are lacking. To evaluate its mitigation potential, we monitored the GHG balance of a poplar ( Populus ) SRC in Flanders, Belgium, over 7 years comprising three rotations (i.e., two 2 year rotations and one 3 year rotation). In the beginning—that is, during the establishment year and during each year immediately following coppicing—the SRC plantation was a net source of GHGs. Later on—that is, during each second or third year after coppicing—the site shifted to a net sink. From the sixth year onward, there was a net cumulative GHG uptake reaching −35.8 Mg CO 2 eq/ha during the seventh year. Over the three rotations, the total CO 2 uptake was −51.2 Mg CO 2 /ha, while the emissions of CH 4 and N 2 O amounted to 8.9 and 6.5 Mg CO 2 eq/ha, respectively. As the site was non‐fertilized, non‐irrigated, and only occasionally flooded, CO 2 fluxes dominated the GHG budget. Soil disturbance after land conversion and after coppicing were the main drivers for CO 2 losses. One single N 2 O pulse shortly after SRC establishment contributed significantly to the N 2 O release. The results prove the potential of SRC biomass plantations to reduce GHG emissions and demonstrate that, for the poplar plantation under study, the high CO 2 uptake outweighs the emissions of non‐CO 2 greenhouse gases.