We suggest a new and general model to describe the effects of temperature (T) and pH on the catalytic activity of enzymes. Despite the abundance of models to describe those effects, the current proposals are unsatisfactory, except for specific experimental cases in which the interactive mechanism between the two variables does not exist. For both variables, our solution analyses the activated and deactivated phases of an enzyme as phenomena of different nature. The system is described with independent probability functions. The interactive effects between T and pH are introduced with simple auxiliary functions. These functions describe the variations induced by each variable in the parameters that define the effects of the other. The structure of the resulting equation is, in theory and practice, very regular, which facilitates its use, and it is highly descriptive in different scenarios with or without interactive effects. The model was tested on three different enzymatic systems which are specifically designed to produce data for the evaluation of the effect of T and pH on the enzyme activity (A). Afterwards, our model was validated using results from other authors. Briefly, the authors found that: (1) other available models that were compared with our proposal were inefficient and in all cases our model provided the only statistically consistent solution; (2) in four cases, the enzymatic activity could only be explained if interactive effects are accepted; (3) synergy and antagonism concepts for the interaction between T and pH were described and classified; and (4) our solution is universal and independent of the structure of an enzyme and the reaction concerned.