We present an additive manufacturing technique for deposition of nanotwinned (nt) metallic nanostructures. Nt metals offer remarkable mechanical and electrical properties compared to their nanocrystalline (nv) counterparts. Three dimensional (3D) freestanding nt-Cu structures with various geometries were fabricated using localized pulsed electrodeposition (L-PED) at the tip of an electrolyte containing glass capillary as nozzle. FIB and TEM analysis confirmed the presence of coherent twin boundaries (TBs) within the 3D printed Cu. The material and mechanical properties of the printed structures were investigated, and compared to nc-Cu structure printed using the same technique under direct current (DC). The results revealed that the printed copper was high quality and mostly free of impurities and defects. The mechanical properties of the 3D printed nt-Cu were characterized using in-situ SEM compression tests of the wires with sub-micron diameter. The results showed a flow stress of over 960 MPa, which is notably high for an additively manufactured Cu structure. This capability will be advantageous in different nanotechnology applications, in particular for 3D nanoscale electronic devices and sensors.