The benzoxazine system reported in this work, coded polyBH-A, is the second benzoxazine vitrimer to be successfully synthesised by the cost-effective solventless one-pot method involving Mannich condensation, with the advantage of being the first high-temperature benzoxazine vitrimer formulated using this strategy. It features a 𝑇 𝑔 of 155°C, a glass modulus of 3.6 GPa, high fire retardancy as indicated by an LOI of 40.5%, relatively high thermal stability with Td5% of 293°C. PolyBH-A has a 𝑇 𝑣 of 78°C, which is below its 𝑇 𝑔 , meaning that a fast reversible bond exchange occurs with the onset of 𝑇 𝑔 . Thus, polyBH-A can be reprocessed at 190°C, following a fast stress relaxation enabled by reversible disulphide bond exchanges. The properties of polyBH-A reported in this work position it as a functional polymer for a broad spectrum of functionalities, such as self-healing, high-temperature, fire retardancy applications for aerospace, which aligns with the future requirements for matrix system of sustainable composites for the aerospace, marine and energy sectors.