High energy density capacitors are critically important in advanced electronic devices and power systems since they can reduce the weight, size and cost required to meet a desired application. Nanocomposites hold strong potential for increasing the performance of high power energy sources; however, the energy density of most nanocomposites is still low compared to commercial capacitors and neat polymers. Here, we develop a new synthesis method for the growth of high aspect ratio barium titanate nanowires (BaTiO3) nanowires (NWs) with high yield. High energy density nanocomposite capacitors are fabricated using surface-functionalized high aspect ratio BaTiO3 NWs in a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) matrix. At a 17.5% volume fraction, the nanocomposites show more than 45.3% increase in energy density above that of the pure P(VDF-TrFE-CFE) polymer (10.48 J/cc compared to 7.21 J/cc) at electric field 300 MV/m. This value is significant and exceeds those reported for the conventional polymer-ceramic nanocomposites; it is also more than seven times larger than high performance commercial polypropylene capacitor (1.2 J/cc at 640 MV/m). In addition, our nanocomposite capacitor has a maximum power density as high as 1.2 MW/cc occurring only 1.52 μs after the start of discharge. The findings of this research could lead to enhanced interest in nanowires based nanocomposites due to their potential for achieving next generation energy storage devices.