Tantalum (Ta) is a body-centered cubic (bcc) metal at ambient conditions and up to its melting point along the principal Hugoniot; however, direct melting temperature measurements are limited. We have developed a technique to measure the surface thermal state of a thin Ta coating shock-released onto a transparent window by combining reflectivity, velocimetry, and pyrometry. Ta is initially shocked into the solid-liquid coexistence and liquid phases, and its shock-released and subsequent reverberated temperature-pressure states are measured. Simultaneous x-ray diffraction is performed on the reverberated state, and the bcc phase is observed off-Hugoniot at 142 GPa. Shock-released and reverberated states bounded by the solidus and liquidus constrain the melting temperature up to 142 GPa and 5880 K between low-pressure diamond-anvil-cell data and high-pressure Hugoniot data. This provides a framework for measuring the temperature along phase boundaries for materials under laser-driven dynamic compression.