They were both born in Dublin, of a French father and an Irish mother. The parents removed to France in 1818, and there the brothers received a careful scientific education.
The younger Abbadie spent some time in Algeria before, in 1837, the two brothers started for Ethiopia, landing at Massawa in February 1838. They visited various parts of Ethiopia, including the then little-known districts of Ennarea and Kaffa, sometimes together and sometimes separately. They met with many difficulties and many adventures, and became involved in political intrigues, Antoine especially exercising such influence as he possessed in favor of France and the Roman Catholic missionaries. After collecting much valuable information concerning the geography, geology, archaeology and natural history of Ethiopia, the brothers returned to France in 1848 and began to prepare their materials for publication.
Arnaud paid another visit to Ethiopia in 1853.
The general account of the travels of the two brothers was published by Arnaud in 1868 under the title of Douze ans dans la Haute-Ethiopie.
Both brothers received the grand medal of the Paris Geographical Society in 1850.