In 1920 he was sent to the United States as a diplomatic representative of the Western Ukrainian government and settled in Philadelphia, where he edited the Ukrainian newspaper Ameryka. Tsehelsky was one of the founders of the Ukrainian Congress Committee of America, a union of 20 Ukrainian organization within the United States.
148: Dr. Lonhyn Tsehelsky, the western Ukrainian negotiator with the Kiev government and primary author of the Union between the West Ukrainian Republic and the Kiev-based Ukrainian People's Republic, expressed shock at the actions of the "rabble" (holota) when the Ukrainian People's Republic came to power.
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Under him was the State Secretariat, whose members included Kost Levytsky (president of the secretariat and the Republic's minister of finance), Dmytro Vitovsky (head of the armed forces), Lonhyn Tsehelsky (secretary of internal affairs), and Oleksander Barvinsky (secretary of education and religious affairs), among others.