Kammala jumla mai zuwa: Daga Eton, Grigg ya shiga rundunar sojojin Birtaniya kuma an ba shi izini a matsayin na biyu a cikin rundunar mahaifinsa, Grenadier Guards, a 1943 a lokacin yakin duniya na biyu (1939 <unk> 1945). Yayin da yake cikin Sojojin Burtaniya, Grigg ya yi aiki a matsayin jami'in Tsaro a Fadar St James da Windsor Castle, Berkshire, kuma ya ga aikin a matsayin kwamandan kwamandan a cikin 1st Battalion, Grenadier Guards, wani ɓangare na 5th Guards Armored Brigade na Guards Armored Division, a kan sojojin Jamus a
Faransa da Belgium. A karshen yakin, ya zama jami'in leken asiri.