An experimental investigation was performed to study the formation of secondary flow structures due to the interaction of a finite-span synthetic jet with a three-dimensional boundary layer over a finite and swept-back wing configuration (cross-sectional profile of the NACA 4421, aspect ratio of 4 and sweep back angle of 30°). The investigation was carried out at a chord based Reynolds number of 105, two angles of attack of 9° and 15.5°, and two blowing ratios of 0.8 and 1.2. Stereoscopic particle image velocimetry (PIV) data were collected around a single synthetic jet actuator in the mid-span of the swept-back wing configuration. The effect of the blowing ratio was analyzed based on the three-dimensional flow field using time-averaged and phase-averaged statistics. Detailed boundary layer profiles show the actuation effects in cases where the jet is introduced to locally attached or separated flow fields, which are determined by the model’s angle of attack. Similar to the interaction of a synthetic jet with a flow over an unswept wing, the flow field in the vicinity of the synthetic jet orifice becomes highly three-dimensional with very distinct secondary flow structures. The flow field is governed by the superposition of two kinds of flow structures: (1) spanwise structures that are generated along the orifice’s span due to the synthetic jet’s vortex pairs and (2) streamwise structures that are associated with the finite span of the jet (edge vortices). These flow structures are formed almost immediately downstream of the synthetic jet orifice and evolve into a well-organized three-dimensional flow field farther downstream.