This investigation characterizes the fracture behavior of a dissimilar weldment comprising E2209 duplex stainless steel as a weld metal and the low alloy steel 20MnMoNi55 as a base metal. The microstructure of the base metal consisted of bainitic structure while the weld metal comprised ferrite and austenite phases. Instrumented impact testing was employed to determine the fracture behavior at temperatures between -196 and 300 C. The results showed that the base metal and the duplex weldment exhibited distinct ductile to brittle fracture transition behavior. The base metal displayed much higher upper shelf energy (USE) level than that of the duplex weldment (130 vs. 80 Joule), designating superior resistance to ductile fracture at high test temperatures. By contrast, the duplex weldment exhibited a greater deal of resistance to brittle fracture at low test temperatures. That was manifested by a lower value of the ductile to brittle transition temperature (DBTT) of the duplex weldment against that of the base metal (-75 vs. 25 C). In addition, the brittleness temperature (the temperature at which complete brittle fracture features prevail) was much less for the duplex weldment than the base metal (-100 vs. -25 C). Furthermore, the cleavage fracture stress as computed from the dynamic yield strength values determined at the brittleness temperature gave values of 2650 and 1890MPa for the duplex weldment and the base metal, respectively. The results were substantiated by the load–time traces, derived from the instrumented impact tests at different temperatures as well as the pertinent fracture surface morphologies.