A four-component relativistic method for the calculation of NMR shielding constants of paramagnetic doublet systems has been developed and implemented in the ReSpect program package. The method uses a Kramer unrestricted non-collinear formulation of density functional theory (DFT), providing the best DFT framework for property calculations of open-shell species. The evaluation of paramagnetic NMR tensors (pNMR) reduces to the calculation of the electronic g tensors, hyperfine coupling tensors and NMR shielding tensors. For all properties, modern four-component formulations were adopted. The use of both restricted kinetically and magnetically balanced basis sets along with gauge-including atomic orbitals ensures rapid basis set convergence. These approaches are exact in the framework of the Dirac-Coulomb Hamiltonian, thus providing useful reference data for more approximate methods. Benchmark calculations on Ru(III) complexes demonstrate the good performance of the method in reproducing experimental data and also its applicability to chemically relevant medium-sized systems. A decomposition of the temperature-dependent part of the pNMR tensor into the traditional contact and pseudocontact terms is proposed.