A gauge-origin invariant formulation of the frequency-dependent Verdet constant V(omega) of magneto-optical rotation and of the Faraday B term of magnetic circular dichroism for coupled-cluster wave functions is derived within the framework of variational response theory. Working expressions suitable for implementation in ab initio program packages are presented. These expressions have a structure similar to that of the expressions for the first hyperpolarizability and the two-photon transition moment, respectively, for the Verdet constant and the B term. The approach is general and can easily be extended to other similar frequency-dependent properties as well as to other wavefunction models. Pilot results at the CCSD level are presented for V(omega) of HF and H-2.