As one of the fundamental forces exerted by fluid on a solid surface, lift is commonly recognized for sustaining flight. However, lift is also widely exploited in the propulsion and maneuver of natural and engineered systems. This dissertation investigates the role of lift in optimal, high-performance propulsion and maneuvering of natural flyers and swimmers, through a combination of experimental approaches, scaling analysis, and hydrodynamic modeling. Beginning with biological propulsion using flapping motion, in which the leading-edge vortex (LEV) is central to the unsteady lift that generates the majority of the propulsive force, this dissertation generalizes the dimensionless vortex formation time from the perspective of LEV circulation maximization. The generalized vortex formation time scales the duration of vorticity injection into the LEV with the rate of injection and the maximum circulation allowed inside of it. By applying this scaling to previously reported animal cruising flight of 28 species, we show that the generalized vortex formation time is consistent across different animals and flight conditions. This finding suggests a fundamental principle underlying the complex wing kinematics of diverse biological flyers, advancing the understanding of propulsion using unsteady lift. In addition to biological flight, aquatic animals also exploit lift-based thrust through their highly adapted morphology and kinematics to achieve high-speed swimming. This dissertation next investigates the propulsion mechanism of surface-dwelling whirligig beetles (