Spacecraft formation flying is a fast improving technology for space missions and while a lot of work has been conducted on spacecraft formation flying control, very few of these algorithms have been validated on flight hardware or through hardware experiments. The L1 adaptive control algorithm is a promising algorithm that can deal with various model uncertainties in real time. As such, this work focuses on the design, simulation, implementation and validation of the L1 adaptive controller for spacecraft formation flying. The L1 adaptive controller is designed and the projection type and piecewise-constant adaptive laws are investigated. The on-orbit simulations are conducted for three dynamics models and the results are discussed. The L1 adaptive controller is shown to have superior performance with significantly lower control forces when compared to a PD controller. The L1 adaptive controller is then experimentally validated using Carleton's SPOT facility.