The originality of this study lies in the real-time monitoring of the crosslinking steps of the polyester resin during the Liquid Resin Infusion (LRI) process of polymer-matrix composites (PMC) by a simple measurement of the electrical capacitance variation of a PZT (Lead Zirconate Titanate) transducer embedded into the heart of the fibrous stack. Three mass rates of a Methyl Ethyl Ketone Peroxide (MEKP) hardener were tested (1wt%, 1.5wt% and 2.5wt%). The electrical capacitance showed a very sensitivity to the crosslinking kinetics while identifying the key steps of the physicochemical transitions of the thermosetting matrix. To identify the promising potential of the PZT transducer as a real-time curing assessment tool of the thermosetting resins, and understand its capacitance signature, the LRI device was multi-instrumented by various non-destructive testing (NDT) techniques such as acoustic emission (AE) and infrared thermography (IRT). The obtained NDT results are confronted with the ones conducted using the oscillatory rheology tests. The agreement between the two types of results (NDT and rheological) allows determining the gelation and vitrification phases of the polyester resin impregnating six plies of 2/2 twill glass fabrics.