Born in the Kingdom of the Two Sicilies to a family of noble Swiss heritage, he spent his early adulthood in the British colonies of Australia and New Zealand before settling in Canada in 1895.

When Anthony was three years old, his father was killed at Palermo while fighting for Giuseppe Garibaldi during the Expedition of the Thousand; his family took refuge in Malta for much of the rest of the rebellion.

[3] He spent several years working for the British colonial governments in what is now Australia and New Zealand in this capacity, before voyaging to the United States to visit his sister.

[1] There he married Ida Eberhard, with whom he had three children: Arthur (1896–1971—born in Ollon because of his father's distrust of the young Canadian medical profession[2]), Edgar (1897–1968), and Richelda (1898–1944).

[4] De Rosenroll's prominence was such that, when Wetaskiwin received a seat in the Legislative Assembly of the Northwest Territories beginning with the 1898 election, he was acclaimed to it.

[8] Whether he declined their entreaties or was defeated is unclear, but the nominated Liberal candidate was James McCrie Douglas, who was elected by acclamation.