<p>The co-pyrolysis of tea seed shell (TSS) and low-rank coal (LC) offers a promising route for the synergistic valorization of biomass and coal. Thermogravimetric analysis (TGA) and fixed-bed reactor experiments were conducted to examine thermal degradation behavior, reaction kinetics, and product distribution. Comparisons between experimental and theoretical mass loss, product yields, and bio-oil compositions confirmed significant synergistic effects. TGA was applied to examine the thermal degradation behavior of individual and blended samples at multiple heating rates. Kinetic parameters determined by the Coats–Redfern (CR) method revealed a significant reduction in activation energy (<i>E</i>_a) during co-pyrolysis, decreasing from 160.97 to 143.45&#xa0;kJ mol⁻¹ (first-order) and from 193.97 to 177.46 kJ mol⁻¹ (1.5-order) with increasing TSS ratio. Fixed-bed experiments further revealed the influence of TSS-to-LC ratio, temperature, and residence time on product yields. The findings indicated that co-pyrolysis promoted the yields of gaseous and solid products over liquid yield, with optimal liquid production at 500&#xa0;℃. Prolonged residence time adversely affected liquid yield. GC–MS analysis indicated that co-pyrolysis enhanced the generation of phenolic and ketonic compounds and reduced oxygenated species, thereby improving bio-oil quality. SEM and FTIR characterization showed that co-pyrolyzed bio-char developed a distinct porous morphology and enhanced oxygen-containing functional groups. These results offer valuable perspectives for the design and optimization of co-pyrolysis systems involving biomass and coal.</p> Graphical abstract <p></p>