Rubuta ci gaba don wannan sakin layi - Daga 1805 zuwa gaba, Saint-Hilaire zai ci gaba da yin aiki a cikin "Grande Armée", yana riƙe da umarnin rarrabuwa daban-daban. A cikin 1805, ya umurci wani rukuni a cikin Marshal Jean-de-Dieu Soult's IV Corps a lokacin Yaƙin Ƙungiyar ta Uku da kuma a yakin Austerlitz
, ya jagoranci kai hari a kan Pratzen plateau, ya sami mummunan rauni a farkon harin amma duk da haka ya ci gaba da jagorancinsa har zuwa karshen yakin. Tsakanin 1806 da 1807, ya yi yaƙi da bambanci a Jena, Eylau da Heilsberg. An sanya shi Count na Daular a 1808 kuma ya sami umarnin rarrabuwa a cikin Sojojin Jamus, wanda zai yi yaƙi da kudancin Jamus da Austria. A ranar 22 ga Afrilu, 1809, Saint-Hilaire ya yi fice a gaban Napoleon a yakin Eckmühl.