The structure and mobility of a<001> dislocations in the β _o phase of an intermetallic TNM-TiAl alloy produced by Spark Plasma Sintering were investigated by transmission electron microscopy. We find that these dislocations are dissociated into two identical superpartial dislocations separated by a stacking fault. Furthermore, a<001> dislocations are elongated along their screw orientation and anchored at small pining points assumed to be nano-sized precipitates of the ω _o phase. In situ room temperature straining experiments show that dislocation propagation occurs through jumps between these elongated configurations.