This paper presents a novel method for providing temperature feedback to the control system of an induction welder during the joining of thermoplastic composite components. Thermoplastic composites are attractive due to their ability to be re-heated and melted repeatedly without degrading the strength of the materials. This enables joining components via fusion bonding or welding, bypassing mechanical fasteners or adhesive bonding completely. In order to ensure a successful joint, the relevant process parameters need to be dialed in and controlled, for specific levels and durations. Induction welding has the advantage of applying a very localized heat, minimizing geometrical distortion of the parts being joined. For the induction welding processes, current and pressure are controlled in an effort to achieve the appropriate temperature at the weld surface with sufficient force to join the two components. Thermocouples are the typical sensors used for temperature measurements, but their size prevents them from being accepted as an inclusion in the final part. As a viable alternative, high definition fiber optic sensing (HD-FOS) is explored as a method for providing a temperature measurement every 1.3 mm along the joint. The small form factor of the sensor lends itself to permanent embedding within the final part. In this work, a high-definition fiber optic sensor is used to provide spatially dense temperature measurements within an induction weld. A control scheme is set up to use the sensor’s measurements as feedback to the controller and to adjust the settings accordingly. This functionality is demonstrated in a dynamic thermoplastic weld setup where the sensor is sandwiched in a lap shear joint configuration. The strength of this weld is evaluated after manufacture and correlated to in-situ temperature measurements. It is shown that HD-FOS could significantly benefit the quality of the final composite part by providing spatially resolved in-situ feedback to the control system to insure uniform temperature profiles at the weld zone and proper processing conditions for each production part.