Friction stir welding (FSW) was investigated for producing joints of alloy PM2000 with welding speeds from 1 to 3 mm/s. The effect of welding speed on the microstructures and mechanical properties of the joints is analyzed in detail. Lower welding speeds result in fully penetrated PM2000 FSWed joints, while higher welding speeds lead to lack of penetration and small defects at the retreating side. The grain size in the stirring zone is not uniform, and abnormal grain growth in the onion rings structure was detected. The PM2000 FSWed joints showed good mechanical properties, i.e., tensile strength of 97% of the base material with even 6.7% higher elongation was obtained. As typical for FSWed ODS joints, the failure was located in the thermo-mechanical affected zone. In this regard, the stirring zone exhibited an impact toughness of up to 300% compared to the base metal owing to the grain refinement, illustrating the superior performance of joints of PM2000 produced by FSW.