Receptor-mediated signal transduction modulates complex cellular behaviours such as cell growth, migration and differentiation. Although photoactivatable proteins have emerged as a powerful tool for controlling molecular interactions and signalling cascades at precise times and spaces using light, many of these light-sensitive proteins are activated by ultraviolent or visible light, which has limited tissue penetration. Here, we report a single-walled carbon nanotube (SWCNT)-assisted approach that enables near-infrared light-triggered activation of transforming growth factor ? (TGF-?) signal transduction, an important signalling pathway in embryonic development and cancer progression. The protein complex of TGF-? and its latency-associated peptide is conjugated onto SWCNTs, where TGF-? is inactive. Upon near-infrared irradiation, TGF-? is released through the photothermal effect of SWCNTs and becomes active. The released TGF-? activates downstream signal transduction in live cells and modulates cellular behaviours. Furthermore, preliminary studies show that the method can be used to mediate TGF-? signalling in living mice.