Biocalorimetry is a process analytical tool extensively employed to measure metabolic heat in order to track cellular activity. To eliminate the inherent demerits in conventional biocalorimeters, an advanced bench-scale heat compensation fermentation biocalorimeter was designed. Improvement in calorimetric signal sensitivity for bioprocess monitoring was achieved by ensuring isothermal condition in the reactor, by operating two independent proportional, integral, and derivative (PID) controls in tandem. Significant reduction in heat loss to the environment was accomplished by incorporating a secondary cascade loop into the cryostat controller. Nonbiological heat measured under different process conditions was calibrated and taken into account as part of the dynamic heat balance. Sensitivity of the system was further improved by incorporating two individual theromostating setups in the reactor housing, viz, a preheated bubble column and a circulating thermal bath fluid in the head plate. Sensitivity and stability of the calorimetric signal were improved to 6.73 mW/L and 0.43 mW/(L h), respectively. The performance of the developed calorimeter was evaluated via real-time monitoring of hyaluronic acid (HA) fermentation by S. zooepidemicus MTCC 3523 and aerobic growth of P. pastoris GSM 115, respectively. The calorimetric signals fingerprinted the changes in cellular metabolism and process behavior with viable precision. Experimentally determined oxy-calorific coefficients, for HA fermentation (684.4 kJ/mol) and P. pastoris growth (471.6 kJ/mol), were in good agreement with theoretical predictions, which validated the reliability and reproducibility of the developed application. Therefore, the developed high-sensitivity calorimeter offered a wide scope for its application as a process analytical technology (PAT) tool for bioprocess monitoring.