Kammala wannan jumla: Grasett shi ne ɗan na uku na Reverend Henry James Grasett, Rector na St. James Cathedral a Toronto, da Sarah Maria Stewart. An koyar da shi a makarantar sakandaren Toronto da kuma a Leamington College for Boys a Ingila. A shekara 19, ya koma Kanada kuma ya shiga rundunar soja ta Kanada. Ya yi yaƙi a tsibirin Niagara a lokacin
Fenian na 1866 tare da 2nd Battalion, Volunteer Militia Rifles na Toronto, A 1867, ya shiga rundunar sojojin Birtaniya da ke aiki tare da Royal Canadian Regiment a Kanada da Ingila kuma ya tashi zuwa matsayin laftanan lokacin da ya yi ritaya zuwa Toronto a 1875, inda ya zama abokin tarayya a kamfanin jigilar kayayyaki da 'yan kasuwa. A shekara ta 1885, an ba shi mukamin Laftanar Kanal a cikin 'yan bindiga kuma ya zama kwamandan Battalion na 10 na Royal Grenadiers wanda ya yi yaƙi da yawa a lokacin Tawaye na Arewa maso Yammacin 1885.