The n-type half-Heusler TiNiSn is very promising for thermoelectric applications in the medium temperature range. However, the synthesis of TiNiSn often involves long annealing times (up to several weeks) to obtain a single phase, which is a major barrier to scaling-up. In this work, TiNiSn was synthesized by a combination of arc-melting, ball-milling and spark plasma sintering. The obtained samples with diameters up to 30 mm had high-purity, high-density and fine-grains. Without the need for an annealing step, the total synthesis time was significantly shortened. Addition of Cu was used to optimize the thermoelectric properties of TiNiSn, and a maximum figure of merit of 0.6 was achieved at 773 K. The fast and scalable synthesis of TiNiSn with good thermoelectric performance presented in this work opens up the possibility of industrial scaling-up.