Many high-impact invaders of temperate deciduous forests of Eastern North America exhibit extended leaf phenology compared to native species, with leaf emergence occurring earlier in the spring and abscission occurring later in the autumn. This observation indicates that extended phenology may be an important invasion mechanism for this system. However, most evidence that extended leaf phenology drives species invasion is anecdotal, and most studies that directly address the role of leaf phenology in invasion focus solely on increased invader growth. Beyond increasing invader growth, extended leaf phenology may drive invader impact on natives by (1) facilitating resource competition through nutrient pre-emption and shading, (2) altering production of secondary chemicals by invasive plants, (3) altering apparent competition dynamics mediated by native herbivores, (4) allowing temporal enemy escape, and (5) altering behaviour of native pollinators. I review current evidence from the literature regarding each of these possible consequences of extended invader phenology and emphasize the need for experimental manipulations to measure the extent to which extended leaf phenology mediates impact on the native community. Understanding the importance of leaf phenology in species invasion will facilitate prevention of future invasions while elucidating the role of seasonality in shaping species interactions.