In 2008 United Kingdom adopted an ambitious target to reduce its greenhouse gas emissions by 80% by 2050, compared to the levels of 1990. This is an unprecedented challenge to the power sector and multiple energy-environment-economic modeling activities have been undertaken to inform the energy policy to deliver this low-carbon transition. The role of governance, choices and strategies of the key actors is increasingly acknowledged as an influential determinant of such transition, but traditional energy-environment-economic models can hardly analyze these aspects. This paper proposes a methodological approach to integrating the governance aspects into energy-environment-economic modeling. In the Realizing Transition Pathways project three qualitative storylines of governance were developed through expert and stakeholder engagement. "Market Rules" storyline envisions that market will deliver low-carbon energy transition. "Central Coordination" storyline envisions increased role of the government in shaping this transition. "Thousand Flowers" storyline envisions the wider civic society leading through bottom-up initiatives. These three qualitative storylines are then translated into a range of modeling assumptions for the D-EXPANSE model (Dynamic version of EXploration of PAtterns in Near-optimal energy ScEnarios). D-EXPANSE has the structure of a bottom-up energy-environment-economic model, but is more flexible and allows for systematic exploration of large numbers of power system transition pathways that are cost-optimal and near optimal. Every governance storyline is thus represented by a large number of quantitative pathways and this provides unique insights into the influence of governance on the future UK power system transition.