Ordered block copolymer thin films are of interest in applications requiring 10nm lengthscale patterns ranging from nanolithography to organic photovoltaics. These applications require not only regularly sized and shaped nanodomains, but also rely on the details of the structure. For example, the optimization of organic photovoltaics made from conjugated polymers relies crucially on the details of the structure and connectivity on the lengthscale of an exciton diffusion length (10nm). Electric, surface, and shear fields have all been suggested to gain the necessary control over nanostructure orientation and position. Implementation of these external fields, however, requires special sample geometries which complicate application. Magnetic fields are routinely used to control order in liquid crystals of arbitrary sample geometry, but classical block copolymers lack sufficient diamagnetic anisotropy to allow magnetic field alignment. We demonstrate the alignment of a conjugated rod-coil block copolymer in a magnetic field to create long range order on both the liquid crystalline (1nm) and block copolymer (10nm) lengthscales. The liquid crystalline director of the conjugated block aligns parallel to the magnetic field and the block copolymer interface aligns perpendicular to it, indicating that alignment relies heavily on the diamagnetic anisotropy of the rod. As a result, a single crystalline array of block copolymer domains of a controlled orientation can be formed in samples of arbitrary geometry.