The study investigates the thermal properties of a suspended metallic single-wall carbon nanotube (SWNT) by extracting its thermal conductance from high-bias electrical characteristics over a temperature range of 300–800 K. The SWNT, with a length of 2.6 μm and a diameter of 1.7 nm, exhibits a thermal conductance of approximately 2.4 nW/K and a thermal conductivity of nearly 3500 Wm^-1K^-1 at room temperature. A subtle decrease in thermal conductivity, steeper than 1/T, is observed at the upper end of the temperature range, attributed to second-order three-phonon scattering between two acoustic modes and one optical mode. The method involves direct self-heating of the nanotube under high-bias current flow, leveraging the relationship between the SWNT lattice temperature and phonon-limited electrical transport. The study also discusses sources of uncertainty and proposes a simple analytical model for the SWNT thermal conductivity, including length and temperature dependence. This work provides the first empirical picture of SWNT thermal conductivity in the 2.6–2.8 μm length range and the 100–800 K temperature range, complementing existing data and representing the first high-temperature study of SWNT thermal properties.The study investigates the thermal properties of a suspended metallic single-wall carbon nanotube (SWNT) by extracting its thermal conductance from high-bias electrical characteristics over a temperature range of 300–800 K. The SWNT, with a length of 2.6 μm and a diameter of 1.7 nm, exhibits a thermal conductance of approximately 2.4 nW/K and a thermal conductivity of nearly 3500 Wm^-1K^-1 at room temperature. A subtle decrease in thermal conductivity, steeper than 1/T, is observed at the upper end of the temperature range, attributed to second-order three-phonon scattering between two acoustic modes and one optical mode. The method involves direct self-heating of the nanotube under high-bias current flow, leveraging the relationship between the SWNT lattice temperature and phonon-limited electrical transport. The study also discusses sources of uncertainty and proposes a simple analytical model for the SWNT thermal conductivity, including length and temperature dependence. This work provides the first empirical picture of SWNT thermal conductivity in the 2.6–2.8 μm length range and the 100–800 K temperature range, complementing existing data and representing the first high-temperature study of SWNT thermal properties.