Kammala jumla mai zuwa: Williamson ya dawo cikin lokaci don shiga cikin yakin Vicksburg da kuma Siege na Vicksburg. Bayan faduwar birnin, ya dauki umurnin na 3rd Brigade, 1st Division, XV Corps har zuwa Satumba, 1863 sa'an nan kuma ya umurci 2nd Brigade, 1st Division, XV Corps a yakin Chattanooga. Ƙungiyar Williamson, wanda Peter J. Osterhaus ya umurce shi, an haɗa shi da dakarun da ke karkashin Joseph Hooker kuma ya shiga cikin
Yaƙin Lookout Mountain. An mayar da sashen zuwa rundunar sojojin Tennessee kuma Williamson ya jagoranci Brigade na 2 a lokacin Atlanta Campaign. A yakin Jonesborough ya ji rauni a hannun. A ranar 19 ga Disamba, 1864 ya sami ci gaba na musamman ga brigadier janar na Amurka Volunteers, a ranar 13 ga Janairu, 1865 cikakken ci gaba ga brigadier janar kuma a ranar 13 ga Maris, 1865 ci gaba na musamman ga babban janar na masu sa kai. A taƙaice a lokacin rani na 1865 ya umurci gundumar St. Louis kuma an cire shi daga aikin sa kai a ranar 24 ga Agusta, 1865, amma ya kasance a kan ziyarar dubawa na rundunonin soja a Yammacin kuma bai gano ba har sai ya dawo a watan Oktoba na shekara ta 1865.