He volunteered with Sir Robert Napier, in the British Expedition to Abyssinia.
This was an Irish peerage and did not entitle him to an automatic seat in the House of Lords.
However, in 1900 he was elected an Irish representative peer, replacing the deceased Lord Inchiquin, and was able to take his seat in the upper chamber of parliament.
Their eldest son, the Honourable Raymond de Montmorency was killed in action at the Battle of Stormberg in 1900.
Lord Frankfort de Montmorency died in May 1902, aged 66, and was succeeded in the title by his second son, Willoughby.