hˈɔːɹnɚ wʌzɐ səpˈoːɹɾɚɹ ʌv dᵻmˈændz fɔːɹ ˈaɪɹɪʃ hˈoʊm ɹˈuːl ænd bɪkˌeɪm ɪnvˈɑːlvd wɪððə ɹˈɛbəl fˈækʃənz fɹʌmðə nˈaɪntiːnhˈʌndɹɪd sˈɪkstiːn ˈiːstɚ ɹˈaɪzɪŋ, dʒˈɔɪnɪŋ ðɪ ˈaɪɹɪʃ sˈɪɾɪzən ˈɑːɹmi.
Horner was a supporter of demands for Irish Home Rule and became involved with the rebel factions from the 1916 Easter Rising, joining the Irish Citizen Army.