The increasing deployment of offshore wind turbines in seismically susceptible areas raises scientific interest in the seismic design of offshore wind turbines. This paper evaluates the vulnerability of tension leg platform wind turbines under combined seismic and environmental loads, addressing a critical and underexplored aspect of floating wind energy. The fully coupled three-dimensional model of the soil-pile-tension leg platform system is developed in Abaqus. The soil is modelled as a 3D continuum with the Mohr–Coulomb constitutive model. The study examines a set of 20 earthquakes scaled to 0.1–0.5 g, consists of near field, far field, pulse, and non-pulse-like records with varying rupture distances, shear wave velocities, pulse period, predominant frequencies, and arias intensity to account for uncertainties in seismic records. Peak ground acceleration (PGA) is used as the intensity measure. Initially, fragility surfaces are established by lognormal distribution. Further, vulnerability curves are proposed for the risk assessment of infrastructural systems including rotor, tower, and substructure based on loss estimation approach. The findings indicate that nacelle acceleration and tendon pretension are critical failure modes, exhibiting the highest failure probabilities at low seismic intensity levels. This study provides a more advanced methodology to assess the potential damage and risk under varying seismic intensities, guiding targeted risk mitigation and design strategies that enhance safety and minimize potential losses.