Photopolymerized composites are used in a broad range of applications with their performance largely directed by reaction kinetics and contraction accompanying polymerization. Herein, we demonstrate an instrument capable of simultaneously collecting multiple kinetics parameters for a wide range of photopolymerizable systems: degree of conversion (DC), reaction exotherm, and polymerization stress (PS). Our system consists of a cantilever beam-based instrument (tensometer) that has been optimized to capture a large range of stresses. The sample configuration allows the tensometer being coupled to a fast near infrared (NIR) spectrometer collecting spectra in transmission. Using our instrument design, simultaneous measurements of PS, DC, and exotherm are performed, for the first time, on a commercial composite with ~80 % (by mass) silica particle fillers. This new system is expected to provide new insights into kinetics and property relationships for photopolymerized composites.