This work develops a tunable chirped guided-mode resonant (GMR) filter that has a hybrid splay-twist (HST) liquid crystal as a cladding layer. The GMR filter is a color reflector that strongly reflects light at the resonance wavelength, and its chirped grating structure supports tuning of the resonance peak over a wavelength range of over 50 nm. The HST-LC configuration serves as an achromatic polarization rotator that can rotate the axis of polarization of linearly polarized light by providing effective twist angles in the LC layer under an applied voltage. The HST-LC is used to change the direction of the polarization axis of the light that is reflected by the GMR filter; continuous angles of rotation of ∼90∘ are achieved and the linear polarization is retained under applied voltages. The proposed filter enables an ultrabroadband polarization rotation and still maintains a high degree of linear polarization, which allows more degrees of freedom in spectral and polarization controls.