Structural phase transitions in metals are conventionally described in terms of external pressure and density, while electronic entropy is typically regarded as a secondary correction to the free energy. Here we show that electronic entropy constitutes a thermodynamic control parameter of comparable importance to external pressure in determining structural stability. Using finite-temperature density functional theory, we construct pressure–electronic-temperature phase diagrams for fifteen transition metals spanning the hcp, fcc, and bcc families and systematically investigate the competition between compressive and entropic contributions to the free energy. We find that increasing electronic entropy progressively reshapes the free-energy landscape, reducing structural competition and driving universal trends in phase stability across chemically diverse metals. In contrast, external pressure often acts in opposition, stabilizing structures that are suppressed by electronic excitation. The resulting phase behaviour cannot be understood from pressure alone but emerges from the balance between these two thermodynamic driving forces. Our results establish a general framework for understanding structural transformations in electronically excited matter, extend the conventional pressure–temperature description of metals by explicitly incorporating electronic entropy, and provide quantitative predictions for ultrafast laser and X-ray free-electron laser experiments operating far from equilibrium.