The problem of autonomous descent and landing of a spacecraft on an asteroid mission is addressed in this paper. Most of the existing literature has addressed this problem utilizing optimal control-based guidance or optimal sliding mode-based guidance formulation. However, both of these methods rely on linearizing the nonlinear engagement dynamics and depend on the time-to-go estimate, which is usually difficult to obtain. To obviate these drawbacks, this paper presents a novel sliding mode-based guidance formulation in full non-linearity of the engagement dynamics. Moreover, it also does not depend on the time-to-go estimates. The concept of collision course against a stationary target has been leveraged in this paper to obtain the dynamics of heading error of the spacecraft, which in turn has been utilized in formulating a sliding surface. Another sliding surface has been formulated to control the speed profile over the entire landing time and ensure a sufficiently small terminal velocity of the spacecraft for its soft landing. The simulation study shows the effectiveness of the presented algorithm for a soft landing. © 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.