Today, thermoplastic composites (TPC) particularly based on carbon fibre reinforcements are gaining in importance as lightweight construction material primarily used within the aircraft industry. Thermoplastic matrices offer several benefits such as uncritical and unlimited storage time, a better impact tolerance compared to thermoset matrices, a good ultimate strain performance, reduced crack propagation, excellent chemical resistance, quick forming process availability, recyclability, the availability of customized laminates and matrices and mainly the weldability. Due to increasing batch sizes necessary for the realisation of large scale aircraft projects, e.g. Airbus A350 and Boeing 787, efficient processing techniques providing high automation potentials, high productivity and a high degree of flexibility are required. The method of laser transmission welding presented in this paper reveals a high potential to fulfil these needs. However, the laser welding technique for TPC shows significantly different process characteristics compared to the well established laser welding of unreinforced thermoplastics. The different absorption and heat conduction behaviour of the TPC have an influence on the heat distribution in the joining zone. Welding tests at varying fibre orientation respective to the welding direction are carried out and the results are investigated by lap shear tests, including fraction pattern and cross section evaluation. With a pyrometer, the temperature profile of bead-on-plate weld seams on TPC is detected taking into account the fibre orientation. In addition, a special IR absorber is applied on the surface, and its effect on the temperature profile is studied. Finally, it can be shown that only a pyrometer-based process control can lead to a homogenous weld seam.