Understanding the temperature sensitivity (Q10) of carbon (C) mineralization and priming of organic matter with different stabilities in a soil with aged biochar is required to enable better forecasting of biochar C sequestration potential under a warming climate. Here, we quantified the Q10 and priming of C mineralization in a Vertisol from: (i) newly added labile organic matter (LOM) in the presence of “aged biochars” and (ii) stable (“aged”) native soil organic matter in the presence of aged biochars or new LOM. We also quantified the Q10 of aged biochar-C (BC) or aged soil organic carbon (SOC)+BC mineralization. Leaf litter from Eucalyptus saligna (a source of LOM) was applied at 4% w/w (δ13C −38‰) to a Vertisol (δ13C −14‰), containing either wood, leaf or poultry litter biochar (δ13C −25 to −28‰), and nil biochar (control soil), previously incubated for 4 years. These biochar−soil mixtures and the control soil, with or without LOM, were re-incubated at 10, 20, 30 and 40 °C for 252 days. The results showed that 22–39% of LOM-C, 0.10–2.81% of aged BC and 2.4–77.0% of “aged SOC” mineralized across all temperatures over 252 days. The Q10 of C mineralization increased with decreasing quality of C substrates in the soil, that is, LOM (1.17–1.21) < SOC (1.23–1.66), SOC + BC (1.23–1.60) < aged BC (1.92–2.26). Positive priming of SOC mineralization was greater by LOM (cf. aged biochar), causing a significant decrease in the SOC Q10 at all temperatures. The aged biochars resulted in negative priming of LOM-C mineralization, mainly at 10 °C, with no impact on the LOM Q10. The results suggest that global warming and tropical climates may lower the C sequestration potential of biochar, by reducing its capacity to slow the mineralization of LOM-C, while increasing the mineralization of native SOC.