This paper presents a Linear Matrix Inequality (LMI) tuned PI controller for real-time control of a coupled-tank liquid level system. The proposed approach is based on the transformation of the PI controller design problem to a state feedback controller design problem, which is further solved using convex optimization approach. The model of the coupled tank system has been developed based on system identification technique that employs least square error method (LS) for parameter estimation. The proposed controller algorithm has been applied on the identified model. The performance of the proposed control algorithm has been compared with that of a Ziegler-Nichols tuned PI controller. From both the simulation as well as the experimental results, it is observed that the performance of the proposed PI control is more efficient than the widely used Ziegler-Nichols approach.