‘Jagger’ has been used widely as a parent to develop hard red winter wheat (Triticum aestivum L.) varieties throughout the US southern Great Plains. Jagger has resistance to the stem rust pathogen race TTTTF, which is virulent to many winter wheat cultivars, yet the genetic basis of this resistance was unknown. Marker analysis and resistance to leaf rust and stripe rust demonstrated that Jagger has the 2NS/2AS translocation from T. ventricosum (Tausch) Ces., Pass. & Gilelli. This segment contains resistance genes Sr38, Lr37, and Yr17. Stem rust infection types on Jagger, however, indicated that an additional stem rust resistance gene is present. Jagger is resistant to TTTTF whereas the Sr38 stem rust differential line ‘VPM1’ is susceptible. A BC1F3 population developed from the cross Jagger/2*‘LMPG-6’ was tested with race TTTTF. Resistant and susceptible DNA bulks were genotyped with a custom 9000 SNP Illumina iSelect Bead Chip using bulked segregant analysis. We identified a locus linked with the resistance gene on chromosome arm 4AL, where Sr7 is located. Crosses between Jagger BC1F3 lines resistant to TTTTF and germplasm with Sr7a identified no recombinants, indicating that resistance to TTTTF in Jagger could be conferred by Sr7a. We confirmed the effectiveness of Sr7a resistance to race TKTTF, which caused the stem rust epidemic in Ethiopia from 2013 to 2014. The molecular markers identified in this study may be used to screen for the resistance gene Sr7a and track its presence in breeding programs.