In current research design, optimisation and prototyping of truck cabin seat plate made of thermoplastic GF/PP composite has been performed. In particular study a conventional steel sheet material has been substituted by lightweight thermoplastic alternative. Such a design should enable a possibility of quick one shot manufacturing of composite structure and in addition it provides a significant weight savings. As a basis for redesign serves topological optimisation based on existing metallic part geometry which has been imported in finite elements code for material distribution analysis. The load case corresponding to the car seat pull test ECE-R14 standard has been applied. Optimisation results indicated that composite part could reach 35 % of the initial steel part. However special treatment should be given to areas under front and rear load bearing points in order to prevent them from the local stress concentration. Therefore final seat plate design has reinforcement areas (patches) under the frame fixation points. For validation purposes prototypes have been examined by non-destructive methods comparing experimental and numerical eigenfrequencies and mode shape results. It was confirmed that experimental prototypes has close matching mode shapes and eigenfrequencies values. In addition local loading on the seat plate fragment have been performed prior to general installation of the whole structure in the truck cabin and executing seat pull-out test. Test demonstrated that displacements at the required load level do not exceed design load values.