<p>Optical forces and torques acting on resonant nanostructures smaller than the wavelength of light have attracted interest in nanoscience and nanotechnology. However, experimental characterization at the nanoscale remains challenging due to the diffraction limit of light. Here we present an approach for the three-dimensional measurement of nanoscale optical forces and torques. This is achieved through the optical trapping and precision spatial tracking of a designed microscale structure that contains embedded target nanostructures. Our method enables the confinement and measurement of nanostructure positions and orientations across three translational and three rotational degrees of freedom, independent of the size, shape and material of the nanostructure. Using this method, we observe transverse optical torque on plasmon-resonant nanostructures and reveal that this behaviour is governed by the optical helicity rather than the angular momentum of incident light. This versatile platform advances our fundamental understanding of nano-optomechanical interactions and opens up possibilities for precise optical manipulation and nanoactuator design.</p>