Foamlike aerogel composites based on renewable xanthan gum (XG) and sodium montmorillonite clay (Na+-MMT) have been prepared using an environmentally friendly freeze-drying process. Additionally, the biobased polysaccharide agar was used to improve the properties of XG/clay aerogels. Fourier transform infrared spectroscopy showed molecular interactions between biopolymers and clay in the aerogel composites. A wide range of microstructures and mechanical properties were obtained with a minimal variation in the density by changing the blended ratio of xanthan gum and agar, with particular emphasis on the addition of 2.5% agar to XG/clay aerogels, which significantly enhanced the mechanical properties. Thermogravimetric analysis revealed that clay improved the thermal stability of aerogels; however, the thermal stability of blends of xanthan gum and agar worsened. Flammability was analyzed through cone calorimeter, which suggested xanthan gum/clay aerogels possessed lower flammability than other typical foams. Clay served as a heat and mass transport, which significantly improved the flame retardancy of the base aerogels.