This paper proposes event-triggered adaptive super-twisting algorithm (ETASTA) based guidance law for a planar relative motion, where the line-of-sight (LOS) rate converges to zero or a small neighborhood of zero in finite-time before guidance termination. The guidance law is proposed by taking into account both the maneuvering and non-maneuvering target. Further, a triggering condition is provided using an event-based approach that uses the minimum amount of control while meeting the stability requirements. Using Lyapunov theorem, the stability of the system is guaranteed. Moreover, it is shown that the proposed theory does not exhibit the Zeno phenomenon, since the inter-event time is bounded by a positive quantity. Finally, a numerical example demonstrates the efficacy of the proposed guidance law. © 2022 IEEE.