This thesis focuses on the design of a steam turbine for a biomass power plant and the associated part of the heat balance diagram. Within the heat balance diagram, among other designed components, a heat exchanger for heating water with a capacity of up to 25 𝑀𝑊 was also included. Based on this capacity, the condensing mode, corresponding to a state with zero heating water output, was selected as the turbine design operating condition. This operating mode subsequently served as the reference condition for the detailed design of the turbine and its associated components, such as the sealing system and bearing selection. Considering this heat exchanger, the feedwater tank, and the low-pressure heaters, a steam turbine with three extraction points was initially designed in the thesis. The turbine design itself was divided into the design of the governing stage and the multistage section. For both of these parts, blade profiles, flow-path geometry, velocity and thermodynamic parameters, as well as energy parameters including losses, efficiency, and power output, were determined. Finally, the design characteristics of the stages were evaluated in terms of dimensionless parameters and subjected to a strength analysis. A key outcome of the thesis is a steam turbine consisting of twenty-six stages distributed across five cone-segments, incorporating two uncontrolled extractions and one controlled extraction fitted with a control diaphragm, achieving a total electrical output of 32,14 𝑀𝑊 and an internal efficiency of 82 % at the design condition. The final part of the thesis presents the operating characteristics of the turbine and a conceptual cross-sectional view.