In this study, a fully variable elliptical phase retarder was developed by combining a variable linear phase retarder and a half-wave plate. All three polarization parameters of the elliptical phase retarder (elliptical phase retardation γ, azimuth angle θ, and ellipticity angle ε) were adjustable. Experimental verification was performed by measuring the polarization parameters with a polarizer-sample-analyzer polarimeter. The polarization parameters were set to γ = 120°, ε = 15°, and θ = 20°. The measurement results, γ = 119.838° ± 0.006°, ε = 14.659° ± 0.002°, and θ = 20.084° ± 0.002°, agreed with theoretical prediction.