Accurate density measurements on a binary (argon + carbon dioxide) mixture were carried out at temperatures T = (273.15, 283.15, 293.15, 308.15, and 323.15) K with pressures up to the dew-point pressure or 9.0 MPa, whichever was lower. A two-sinker magnetic suspension densimeter was utilized for the measurements. The composition of the gravimetrically prepared mixture was 0.94951 mole fraction carbon dioxide. Taking the measurement uncertainties in temperature, pressure, density, and composition into account, the relative combined expanded uncertainty (k = 2) in density was estimated to be less or equal 0.043% of the measured density value. Relative deviations of the new experimental data from the GERG-2008 equation of state (EOS) and from the EOS-CG (a recently developed multiparameter EOS optimized for combustion gases) were within 0.95% and 0.18%, respectively. Third-order virial equations were fitted to the new experimental data. The correlated molar masses at different isotherms agreed with the gravimetrically determined one within 0.02%. Values and uncertainties of the second and third virial coefficients and the second interaction virial coefficient for the binary mixture were determined.