[2] He was serving in that post when, on 12 April 1910, Pope Pius X appointed him bishop of the newly erected Diocese of Lipa.

[3] He received his episcopal consecration on 12 June 1910 from Archbishop Ambrose Agius, Apostolic Delegate to the Philippines.

On 30 May 1915, Pope Benedict XV named him to succeed Agius as Apostolic Delegate to the Philippines and made him titular archbishop of Nisibis.

[4] In 1916–17 he visited Japan to investigate the state of religious freedom, granted by the Japanese constitution but in practice the government was intolerant of non-Shinto adherents.

[2] In 1918, when the Holy See and China agreed to exchange representatives, Petrelli was proposed as the pope's emissary, but objections from the French government, which had long exercised control over the Church in mission territories, prevented the exchange.