The development of integrated biorefineries is one of the currently proposed strategies for transforming into a low carbon bio-economy. Although different biorefining technologies can be integrated into host mills such as the Kraft and thermomechanical pulp processes, it is important to select the most appropriate technology taking into consideration the specificities and on-site constraints. In this work, a decision support tool was developed and applied to industrial case studies for biorefinery implementation. Firstly, the tool was used for scenario-based simultaneous analysis of the technical, economic, and environmental impacts in a single platform for different biorefinery implementation strategies. Its robustness and flexibility were demonstrated by two comprehensive industrial cases covering biorefinery transformation strategies for a Kraft pulp corporation involving three sites and a newsprint corporation with two sites. The tool made it possible to elucidate the advantages of lignin recovery implementation at modern and median Kraft pulping sites. Also, it revealed the objective basis for selecting between lignin recovery, hemicelluloses extraction, and thermochemical platforms biorefineries. The most suitable plant capacity for profitability was determined in the case of repurposing a median or average integrated newsprint mill into a biofuel production facility based on the pyrolysis platform. In a modern integrated newsprint mill, it was shown that phenol-formaldehyde (PF) resins production can significantly decrease production costs, diversify the product portfolio, and mitigate risks associated with the core product line.