The challenge in creating stable and dense KNbO3 ceramics is suppressing the K2O volatility that occurs at elevated temperature and avoiding the formation of unwanted phases. This challenge could be addressed by applying a field-assisted sintering technique. Flash sintering was conducted successfully on KNbO3 powder, under applied electric field of 600 V/cm at 750 °C. The linear shrinkage of the sample was approximately 18%, and its density was 95% of the theoretical density. Homogeneous dense samples were obtained, containing grains with similar size to that of the green powder. The stoichiometry ratio of potassium to niobium (K/Nb) remains similar to that of the green powder. Flash sintering is proven here as a process which overcomes the main challenge of sintering ceramics with highly volatile species. In addition to its known advantages, we show here that the process is also a breakthrough in the synthesis of dense stoichiometric KNbO3.