Nutrient availability for tundra wetland vegetation could change drastically due to increasing temperatures and frequency of nitrogen deposition in the Arctic. Few studies have simultaneously examined the response of plant communities to these two pressures over a long period of time. This study aims to assess which driver between global warming and nitrogen deposition is more likely to transform artic wetland vegetation and whether there is a time lag in this response. An annual fertilization experiment simulating these nutrient inputs was conducted for 17 years in the Canadian High Arctic to assess the impact on aboveground net primary productivity, floristic composition, and plant nutrient concentration. While the primary productivity of graminoid was increased slightly by N deposition alone (36% increase), graminoid productivity increased strongly in the global warming treatments simulated by N-P addition (more than a 227% increase). We noted no differences in the primary productivity of graminoids between the 2nd and 5th year of the experiment, but we observed an increase of 203% between the 5th and 17th year in treatments simulating the fertilizing effect of warming. These results indicate that the impact of warming through increasing nutrient availability was greater than those of N deposition alone and promoted the transition from a moss-dominated wetland to a graminoid-dominated wetland. However, this transition was subject to a time lag of up to 17 years, suggesting that increased productivity of graminoids resulted from a release of nutrients via the decomposition of lower parts of the moss mat.