Direct graphene growth on flexible substrates via chemical vapor deposition (CVD) is an attractive approach to manufacturing flexible electronic devices, as it avoids the drawbacks of transferred graphene. To fabricate flexible devices on plastic substrates, the growth temperature must be below ~200 °C to prevent substrate deformation. Here, we report the direct growth of high-quality graphene on flexible substrates at 150 °C with no transfer processes. We show that the high-quality graphene can be directly grown on a variety of substrates via the introduction of an ultra-thin titanium buffer layer, due to perfect lattice matching between titanium and carbon atoms. We further demonstrate that the titanium buffer layers oxidized naturally upon exposure to air after graphene growth do not influence the transmittance and electrical conductivity of graphene. We report theoretical and experimental evidence for large-scale, high-quality graphene grown on in-situ deposited titanium-buffered substrates at 150 °C in a CH4/H2 atmosphere via plasma-assisted thermal CVD. We applied the proposed methodology to fabricate flexible and transparent thin-film capacitors with direct grown top- and bottom-graphene electrodes. These findings could pave the way to the practical exploitation of flexible electronic devices via large-scale, high-quality monolayer graphene grown directly with no transfer processes.