This work develops a strategy for thermoelectric characterization by transient Harman method under nonideal contact and boundary conditions. A thermoelectric transport model is presented that accounts for the effects of thermal and electrical contact resistances and heat transport through electrodes and supporting substrate. Parasitic effects play a large role in controlling the temperature difference across thin thermoelectric films on substrate. Analytical expressions for the temperature difference across the thermoelectric sample are provided to aid in the separate determination of the Seebeck coefficient, thermal conductivity, and electrical resistivity of the sample and to quantify the parasitic effects. The proposed experimental technique employs the Harman method under bipolar current excitation over a wide range of currents to allow Peltier only and combined Peltier and Joule heating effects to control the temperature difference across the sample. Proof of concept experiments were performed on commercial thermoelectric pellets mounted on the original ceramic substrate. In addition to the samples' thermoelectric properties, thermal and electrical contact resistances could be also experimentally determined by this technique.