 Ramba uchiverenga ndima ino - Callwell akaberekerwa muLondon, ari iye oga mwanakomana waHenry Callwell, wokuLismoyne, Ballycastle, County Antrim, nomudzimai wake, Maud Martin, wokuRoss, Connemara. Akadzidziswa nemudzidzisi wechiGermany, uye ipapo paHaileybury, asati apinda Royal Military Academy, Woolwich, muna 1876. Akagadzwa salieutenant muna Ndira 1878, achijoinha bhatiri re3rd Brigade, Royal Field Artillery, yakabva yaiswa muIndia, uye ichishanda mumatanho ekupedzisira eHondo yechipiri yeAnglo-Afghan. Muna Ndira 1881 bhatiri rake rakatamisirwa kuNatal, richisvika panguva chaiyo kuti riite basa rokupedzisira rokurwisa maBoer eTransvaal.. Nokukurumidza pashure pacho Callwell akadzokera kuWoolwich; ipapo mukupera kwa1884 akapasa bvunzo dzekupinda muStaff College, kwaakanga ari mudzidzi kubva munaFebruary 1885 kusvika muna 1886. Akakwidziridzwa kuva kaputeni musi wa 17 Kurume 1886. 