Kammala jumla mai zuwa: Jackson ya fara aikinsa na Sojojin Amurka a matsayin laftana na biyu a Kamfanin K na 1st US Artillery Regiment, yana ci gaba ta Pennsylvania, zuwa Kogin Ohio da Mississippi zuwa New Orleans, kuma daga can sojojin suka tashi zuwa Point Isabel, Texas, kuma aka tura su don yin yaƙi a cikin Yakin Mexico-Amurka daga 1846 zuwa 1848. An umurci umurnin Jackson ya ba da rahoto ga Janar Taylor kuma ya ci gaba nan da nan ta hanyar Matamoros da Camargo zuwa Monterey sannan kuma zuwa Saltillo. Kafin yakin Buena Vista, an umurci umurnin Lieutenant Jackson ya janye daga rundunar Janar Taylor kuma ya yi tafiya zuwa bakin Rio Grande, inda za a canja su zuwa Veracruz. Ya yi aiki a
Siege na Veracruz da yaƙe-yaƙe na Contreras, Chapultepec, da Mexico City, a ƙarshe samun lambobin yabo guda biyu, da kuma rundunar soja na farko na laftanar. A Mexico ne Thomas Jackson ya fara haduwa da Robert E. Lee.