Accurate dew-point, dielectric permittivity, and density measurements of two binary (H-2 + CO2) mixtures with CO2 mole fractions of 0.94638 and 0.74576 were carried out utilizing an apparatus that employs a microwave re-entrant cavity resonator. Isochoric dew-point measurements were conducted at pressures up to 7.1 MPa and temperatures from T = (249.55 to 296.61) K for the (0.05362 H-2 + 0.94638 CO2) mixture and between T = (251.63 and 280.44) K for the (0.25424 H-2 + 0.74576 CO2) mixture. The combined expanded uncertainty with a level of confidence of approximately 95% (k = 2) in dew-point temperature and pressure ranged between (0.016 and 0.065) K and (0.0041 and 0.0177) MPa, respectively. Within 2.5%, the new data were consistent with the predictions of the GERG-2008 equation of state. Measurements of dielectric permittivity in the single-phase vapor region over the temperature range from (273.06 to 313.18) K at pressures up to 8.2 MPa and in the vicinity of the phase boundary were conducted to determine mixture molar densities by applying a method based on the polarizability mixing rule developed by Harvey and Prausnitz. The microwave-determined mixture densities near 5 MPa agree within 0.33% of reported values measured with a precision two-sinker magnetic suspension densimeter; mixture densities near 8 MPa agree within 1.33% of values calculated with the GERG-2008 equation of state.