Historical slender steel towers designed before modern fatigue provisions require evidence-based procedures to assess their remaining fatigue life under wind action. This study presents a time-domain fatigue life estimation procedure and applies it to the 368.5 m Riga TV tower, the tallest structure in the Baltic states, completed in 1989. Because the tower’s materials and construction predate current European standards and its height-varying cross-section and closely spaced modes are not well represented by the simplified structural factor of EN 1991-1-4, synthetic wind load histories were generated according to EN 1991-1-4 and the Kaimal turbulence spectrum, including across-wind vortex shedding represented by a simplified lock-in model, and applied to a parametric global finite element model and refined local models of the critical details. The natural frequencies of the global model agree with those identified from geophone and fiber-optic strain measurements, and the computed bending-stress ranges follow the measured trend over the 2–14 m/s range of recorded mean wind velocities. Fatigue damage was evaluated from rainflow-counted stress ranges with the Palmgren–Miner rule and the S–N curve of EN 1993-1-9. For the assessed weld detail the damage is D = 0.081 for a 50-year reference period and 0.060 over the 37 years of service to date, dominated by across-wind oscillations in the second-mode lock-in range at 7–9 m/s. The main limitations are the simplified treatment of lock-in without aerodynamic damping, the assumed structural damping and weld detail category, and the single meteorological record used for the wind exposure; their influence on the result is discussed. The procedure provides a practical, measurement-supported basis for the fatigue assessment of historical steel towers.