In this study, the problem of -stabilising a general class of second-order linear time invariant systems with dead-time using a proportional–integral–retarded (PIR) controller is considered. The -stability of a system determines the exponential decay in its response. Here the -stability of the closed-loop system is ensured by assigning up to four dominant real roots at . For the tuning of the controller gains an extensive analysis of all the possible allocations of the gains according to the response of the closed-loop system is presented. The D-partition method is used to provide important insight into the problem. As a consequence of this analysis, to achieve the desired decay rate, exact analytic expressions for tuning the PIR controller parameters are given. To illustrate the theoretical results obtained, the under-actuated mechanical system called inverted pendulum is used.