Kammala jumla mai zuwa: An haife shi a ranar 17 ga Maris 1787 ga Charles da Ann Fergusson, an ba Fergusson izini a matsayin mai ba da izini a 1801, a cikin 18th (Royal Irish) Regiment of Foot, kafin a canza shi zuwa 43rd (Monmouthshire) Regiment of Foot, horar da shi a matsayin jarumi mai haske a karkashin Sir John Moore a Shorncliffe. An ba shi mukamin Laftanar a 1804, kuma kyaftin a 1806, ya yi aiki a cikin Light Division a duk lokacin yakin Peninsular. Fergusson ya halarci yakin da aka yi a
Roliça, Vimeiro, (inda ya sami raunuka), da Corunna, inda rundunarsa ta kasance wani ɓangare na ajiyar. Fergusson ya bi 43rd a kan 1809 Walcheren Expedition kafin ya koma yankin Peninsula, yana fuskantar aiki a Kogin Côa, Bussaco, Sabugal, Fuentes de Onoro, da Ciudad Rodrigo da Badajoz, inda ya kasance wani ɓangare na ƙungiyoyin da ke kai hari na 43, yana karɓar raunuka sau biyu. Ya sami lambar zinare don aikinsa a Badajoz. Bayan kyakkyawan aiki a Salamanca a 1812 an daukaka shi zuwa Major ba tare da saya ba, yana ɗaukar matsayi a cikin 79th Foot. An canza shi zuwa 85th Foot, yana ganin aiki a Bidassoa, Nivelle, Nive da Bayonne.