ɪn ˈɔːɡəst nˈaɪntiːnhˈʌndɹɪd fˈoːɹɾi sˈɪks, hˈɔːɹnɚ wʌz ᵻlˈɛktᵻd dʒˈɛnɚɹəl sˈɛkɹətɹi ʌvðə jˈuːnɪfˌaɪd nˈæʃənəl jˈuːniən ʌv mˈaɪnwɜːkɚz ˌɛnjˌuːˈɛm ˌɪntʊ wˌɪtʃ ðə kˈoʊlfiːld jˈuːniənz hæd mˈɜːdʒd.
In August 1946, Horner was elected General Secretary of the unified National Union of Mineworkers (NUM) into which the coalfield unions had merged.