A single-source precursor for the preparation of HfC-SiC ceramics was synthesized via a Grignard reaction using bis(cyclopentadienyl) hafnium(IV) dichloride, trans-1,4-dibromo-2-butene, and (chloromethyl) trimethylsilane as raw materials. The composition, structure, pyrolysis process and high-temperature behavior of the precursor were investigated. The results show that the precursor with a backbone comprising Hf-C, Si-C and CH=CH groups exhibits good solubility in common solvents, such as tetrahydrofuran, dimethylbenzene, and chloroform. Pyrolysis of the precursor at 1000 degrees C yielded a microcrystalline HfC phase with a ceramic yield of 63.86 wt%. The pyrolytic products at 1600 degrees C were HfC-SiC nanocomposite ceramics, which exhibited good thermal stability up to 2400 degrees C. The formation of a (Hf,Si)C solid-solution would be beneficial for densification during the sintering process. The non-oxygen structure, high ceramic yield, homogeneous composition and excellent high-temperature behavior of the pyrolytic products make the as-prepared precursor a promising material for the preparation of high-performance ultra-high-temperature ceramics.