Abstract Self-propagating high-temperature synthesis (SHS) has potential for the efficient production of high melting temperature intermetallics such as Ti5Si3. However, the process is poorly understood due to the difficulty of making in situ observations. In this research, the self-propagating synthesis of Ti5Si3 from furnace ignited elemental samples was studied using high-speed in situ neutron powder diffraction. Diffraction patterns were recorded at 0.9 s time-resolution during heating at >100 K/s. Despite the existence of four other titanium silicides (TiSi2, TiSi, Ti5Si4, Ti3Si) evidence of these or other intermediate phases was not found in either the pre-heating or reaction stages of the process. The reaction is, however, narrowly preceded by the α→β transformation in Ti, which initiates interdiffusion and acts as a trigger for SHS ignition. The formation of Ti5Si3 appears to occur by the direct solid state reaction of β-Ti and Si.