On 1 October 1876 von Garnier joined the Husaren-Regiment „Graf Goetzen“ Nr.

During World War I he served as a division- and corps-level commander of Imperial German troops.

He was in command of 4th Cavalry Division, which was part of the force that moved into neutral Belgium to invest the fortress city of Liege.

In August - September 1915, at the head of the cavalry corps, he led the Sventsyansky breakthrough (Конница в Виленской операции 1915-го).

[6] Взаимодействие конницы с конной артиллерией / Битва Гвардий - https://btgv.ru/history/troops-history/%D0%BC%D0%BE%D0%B1%D0%B8%D0%BB%D1%8C%D0%BD%D1%8B%D0%B5-%D0%B2%D0%BE%D0%B9%D1%81%D0%BA%D0%B0-%D0%B2-%D0%B1%D0%BE%D1%8E/interaction-of-cavalry-with-horse-artillery/