In alignment with the Paris Agreement, Switzerland aims to reach net zero emissions by 2050.According to the recent Climate and Innovation Act, Swiss federal agencies must decarbonize their building portfolios to reach net-zero emissions already by 2040, in advance of the national net-zero targets.In support of these efforts, in this study, we develop an approach to analyze potential decarbonization pathways for a large building portfolio (approx.1000 buildings) owned by a federal agency.First, the impact of different envelope retrofits on demand reduction is evaluated on the building level using CESAR-P simulation software based on EnergyPlus, together with the corresponding costs and embodied emissions.Trade-offs between cost-and emission-optimal solutions are evaluated via multi-objective optimization using the MANGOret model for each building, with the corresponding combinations of building envelope retrofit, heating system replacement, and PV system integration over a time horizon of 15 years.The Pareto optimal solutions at the building level are aggregated to the portfolio level and compared to the point closest to the origin (i.e.zero costs and zero emissions) for each building.The solutions at this point comprise the zero scenario.Additionally, trade-offs between key performance indicators (KPIs) measuring cost-effectiveness of emission reduction, demand and emission intensity, as well as renewable energy generation are assessed.We show that the most favorable cost-effectiveness of emission reduction with respect to the cost-optimal point are achieved with the zero scenario.At the two extremes, cost-optimal solutions rely mainly on heating system replacement and PV system installations to reduce the emission intensity of the portfolio, while emission-optimal solutions include a high share of envelope retrofits to reduce useful heating demand, in addition to energy supply solutions.Additional KPIs can be used by decision-makers to prioritize retrofit interventions across the portfolio, enabling a side-by-side comparison of potential decarbonization pathways.