Wheat production in many countries is threatened by climate change and rising sea levels causing increases in salt-water intrusion in low-lying coastal areas. Large areas of the coastal zone of Bangladesh remain fallow during the dry season primarily due to salinity. It is estimated that 0.86 million hectares of land currently under fallow in the dry season would be suitable for wheat production using varieties with enhanced salt tolerance. This study investigated the impact of salt tolerance Nax genes (Na+ exclusion) on the grain yield of bread wheat grown on saline soils in southern Bangladesh. Nax1 and Nax2 genes were separately crossed into two Bangladeshi bread wheat varieties, BARI Gom 25 and BARI Gom 26, through conventional crossing with marker-assisted selection. The key outcome was strong evidence that both Nax genes have the capacity to lower leaf Na+ concentration in locally adapted bread wheat and consequently deliver improved yields in challenging field environments in southern Bangladesh with moderate to high salinity. The genetic backgrounds of the adapted varieties played a significant role in the expression of these genes. There was a differential response in the phenotypic expression of Nax genes to reduce leaf Na+ levels between the two local varieties selected as recurrent parents and the resultant variation in yield. The average reduction in leaf Na+ concentrations from the third backcrossed lines in the BARI Gom 25 background was about twice that of lines in the BARI Gom 26 background. These same lines typically yielded between 10% and 20% higher than BARI Gom 25 on moderate to high salinity sites, whereas the backcrossed lines in the BARI Gom 26 background yielded similarly to their recurrent parent at these same sites. The contrast in the differential phenotypic expression of the Nax genes evident in the two recurrent parents represented in this study highlights the importance of crossing salt tolerance Nax genes into a range of locally adapted high-yielding genetic backgrounds to identify the greatest potential for improvement in salt tolerance.