Thermoelectric (TE) generators capable of converting thermal energy into applicable electricity have gained great popularity among emerging energy conversion technologies. Biopolymer-based ionic thermoelectric (i-TE) materials are promising candidates for energy conversion systems because of their wide sources, innocuity, and low manufacturing cost. However, common physically crosslinked biopolymer gels induced by single hydrogen bonding or hydrophobic interaction suffer from low differential thermal voltage and poor thermodynamic stability. Here, we develop a novel i-TE gel with supramolecular structures through multiple noncovalent interactions between ionic liquids (ILs) and gelatin molecular chains. The thermopower and thermoelectric power factor of the ionic gels are as high as 2.83 mV K⁻¹ and 18.33 μW m⁻¹ K⁻², respectively. The quasi-solid-state gelatin–[EMIM]DCA i-TE cells achieve ultrahigh 2 h output energy density (E_2h = 9.9 mJ m⁻²) under an optimal temperature range. Meanwhile, the remarkable stability of the supramolecular structure provides the i-TE hydrogels with a thermal stability of up to 80 ℃. It breaks the limitation that biopolymer-based i-TE gels can only be applied in the low temperature range and enables biopolymer-based i-TE materials to pursue better performance in a higher temperature range.