Large-area graphene synthesized by a chemical vapor deposition (CVD) method is promising for a flexible, stretchable transparent electrode but suffers from structural defects such as grain boundaries, which causes to degrade its physical properties. Recently, preparation methods of large-scale growth templates for single-crystalline graphene (SCG) were reported, but the macroscopic properties of SCG have not been adequately examined yet. Here, an SCG-based flexible, stretchable graphene transparent electrode is successfully demonstrated, which shows superior optoelectrical, electromechanical, and barrier properties compared to polycrystalline graphene (PCG)-based transparent electrodes. The result exhibits the grain boundary effect of graphene on soft substrates on a macroscopic scale and a great promise toward realizing a tremendous performance improvement of graphene-based flexible transparent electrodes on a large scale.