The development of high-speed railways is progressing at a very rapid pace worldwide. For example, in the UK, the construction of Phase 1 (225 km) of the HS2 line has now begun, and it will have a maximum operational speed of 360 km/h. In this paper, the performance of a geosynthetic-reinforced soil retaining wall (GRS-RW) is presented for both ballasted track and concrete slab track using full-scale laboratory testing and geotechnical centrifuge modelling. In the full-scale testing, the geo-pavement and railways accelerated fatigue testing (GRAFT II) facility at Heriot-Watt University is used. It operates using six independent hydraulic actuators over three full-size sleepers to simulate the passage of a moving train. The tested GRS-RW structures consist of well-compacted subgrade and a frost protection layer designed to HS2 standards. Results are recorded in terms of deflections, accelerations, total settlement and transient stresses at various locations of the structure model. Whilst the full-scale GRAFT II testing elucidates behaviour of the track and wall, in order to study how the foundation subsoil may interact with the structure, a series of small-scale experiments were carried out in the geotechnical centrifuge by the University of Dundee. By creating small-scale physical models of the GRS-RW and foundation and by increasing gravity, the centrifuge was used to simulate the large induced stresses. Short- and long-term deformations of the wall and foundation were also monitored. Comparisons between the full-scale and centrifuge modelling are presented.