The dissolution and functionalization of cellulose in the DMAc/LiCl system assisted by microwave irradiation is investigated. Cellulose solutions were prepared using mono- and multimodal microwave radiation, as well as using a conventional heating method. The effect of microwave irradiation on the dissolution of cellulose was evaluated by comparison of physical properties such as the viscosity of the resulting solution and the size distribution of the cellulosic chains in solution. We demonstrate that monomodal microwave irradiation allows for a faster and easier dissolution of cellulose, when compared with the use of multimodal microwave irradiation, or conventional heating. Furthermore, we show that monomodal microwave irradiation can be used for a one-pot modification of cellulose undertaken in two steps, first dissolution of the cellulose followed by reaction of the functional groups. The concept is illustrated by the modification of cellulose with lauroyl chloride.