The event-triggered control problem is investigated for nonlinear uncertain systems via a prescribed-time approach. Different from the existing event-triggered control methods that can only achieve bounded or finite-time stability, this article focuses on the prescribed-time stability under the event-based design method. First, a novel prescribed-time stability criterion is presented, which provides explicit theoretical supports and systematic guidelines for addressing the studied problem. Then, we put forward a new method for co-designing the controller and event-triggering mechanism by utilizing the idea of backstepping design. Based on the proposed stability criterion, it is proved that the controller constructed with the new method can regulate the system states to zero in the prescribed-time interval while avoiding the Zeno phenomenon, thus improving the previous prescribed-time stabilization results that are all based on the real-time control signals. Finally, a simulation example is given to show the effectiveness of proposed control strategy.