The paper and pulp industry is the sixth largest consumer of energy in the U.K. Furthermore, the industry produces a significant amount of fibrous sludge and reject waste material, containing high amounts of useful energy. Currently the majority of these waste fractions are disposed of by landfill, land-spread, or incineration. These disposal methods not only present environmental problems but are also very costly. This review explores how paper industry wastes can be valorized into useful energy vectors via advanced thermal conversion routes, thus providing not only a solution for waste disposal but also a means of producing useful sustainable energy at paper mill sites. The scope of this work explores the application of advanced thermal conversion methods (gasification and pyrolysis) for the conversion of secondary fiber paper mill wastes into energy vectors. The order of the paper follows a specific structure. Initially, a detailed description is given concerning which wastes are generated from secondary fiber paper mills. This is followed by a brief review of the state of the art in waste management and energy systems currently used by paper mills. Then, a review on advanced thermal conversion pathways as a solution to the dual issue of waste management and energy generation for secondary fiber paper mills is given, including details regarding the feasibility of integrating them into the current mill infrastructure. Finally, a discussion of the challenges associated with the proposed conversion pathways is given.