The design and application of rubber-based nanocomposites reinforced with hybrid nanomaterials have been receiving extensive attention, yet the right combination values and the synergistic effects are to be fully discovered for many pair particles. In this study, the mechanical, physical, and thermal properties of styrene-butadiene rubber (SBR) nanocomposites holding different contents of carbon nanotube (CNT) and nanodiamond (ND) were measured. The effect of nanoparticles individually and in different hybrid compositions was investigated meticulously to obtain the optimized formulations. The SBR nanocomposites holding nanoparticle concentrations ranging between 1 to 5 phr were fabricated. To get a better insight into the effect of nanoparticles on the SBR properties, bound rubber, tensile, DMA, and thermal conductivity tests were carried out. It was found that hybrid nanocomposites showed uniform dispersion of nanofillers in the matrix through SEM examination. The hybridization of nanoparticles improved mechanical properties such as tensile parameters better than ND and carbon nanotube individually. The synergistic effect of nanoparticles on the thermal conductivity was salient. The nanocomposites holding 5 phr of hybrid nanoparticles possessed thermal conductivity approximately two-fold higher than unfilled SBR nanocomposites and 20% more than nanocomposites with 5 phr content of CNT