Giant exoplanets orbiting close to their host stars are unlikely to have formed in their present configurations<SUP>1</SUP>. These `hot Jupiter' planets are instead thought to have migrated inward from beyond the ice line and several viable migration channels have been proposed, including eccentricity excitation through angular-momentum exchange with a third body followed by tidally driven orbital circularization<SUP>2,3</SUP>. The discovery of the extremely eccentric (e = 0.93) giant exoplanet HD 80606 b (ref. <SUP>4</SUP>) provided observational evidence that hot Jupiters may have formed through this high-eccentricity tidal-migration pathway<SUP>5</SUP>. However, no similar hot-Jupiter progenitors have been found and simulations predict that one factor affecting the efficacy of this mechanism is exoplanet mass, as low-mass planets are more likely to be tidally disrupted during periastron passage<SUP>6-8</SUP>. Here we present spectroscopic and photometric observations of TIC 241249530 b, a high-mass, transiting warm Jupiter with an extreme orbital eccentricity of e = 0.94. The orbit of TIC 241249530 b is consistent with a history of eccentricity oscillations and a future tidal circularization trajectory. Our analysis of the mass and eccentricity distributions of the transiting-warm-Jupiter population further reveals a correlation between high mass and high eccentricity.