Abstract: Presented is a method and system for phase locking a multi-stage parallel fiber amplifier. The method comprises receiving a signal beam from a first stage, in one path of the multi-stage fiber amplifier, onto a fiber that is pumped to produce a saturated signal beam that is then output to a second stage that outputs an amplified beam. A characteristic of the of the saturated signal beam is that its phase and amplitude do not substantially change based on the amplitude of the signal beam input onto the fiber. The method further detects a portion of the amplified beam to produce a phase indication of the amplified beam relative to amplified beams of the other paths of the multi-stage fiber amplifier. The method modulates the pump level of the first stage to control the phase of amplified beam, and further controls the phases of the other amplified beams of the other paths to phase lock the multi-stage parallel amplifier.