The thermal evolution of the electric field-induced birefringence, δ(Δn(E)) vs T, obtained by the Kerr and Pockels electro-optical effects, was characterized in the La-doped Pb(Mg1/3Nb2/3)O3 – PbTiO3 ferroelectric relaxor ceramic system. The measurements were conducted over a broad temperature range (from 100 K to 650 K), using the dynamic Senarmont compensator method. Moreover, through a particular approach to the analysis of both electro-optical effects as a function of temperature, it was possible to determine the characteristic temperatures predicted for the transitions between the paraelectric (PE), ergodic ferroelectric relaxor (EFR), nonergodic ferroelectric relaxor (NEFR), and normal ferroelectric (FE) states of this system.