Originally from northern Italy's Piedmont region, Marengo has spent the past 19 years serving as a Consolata missionary priest in Mongolia.
Pope Francis named him the Prefect of Ulaanbaatar, Mongolia’s apostolic prefecture, in 2020. After a meeting with the pontiff, Marengo said that Pope Francis was “very interested in the … the Church in Mongolia and of the Mongolian people in general.”
“We know how much the pope cares about the entire Church, even those areas where there are not large numbers, indeed precisely where the Church is more in the minority," he said.
Mongolia has a population of about 1,300 Catholics in a country of more than 3 million people. The Prefecture Apostolic of Ulaanbaatar serves the entire country.
While serving as a Consolata missionary in Mongolia, Marengo established a new catechesis program. He told CNA in 2014 that the program sought to form young adults into future catechists by providing lessons in theology and the Church and its mission.
"I believe being a bishop in Mongolia is very similar to the episcopal ministry of the early Church," Marengo said.
"The Church is a very small reality, it is a minority but there is this group of Mongolian faithful who have chosen, with great courage and also a sense of responsibility, to follow the Lord and become part of the Catholic Church."
The first modern mission to Mongolia was in 1922 and was entrusted to the Congregation of the Immaculate Heart of Mary. But under a communist government, religious expression was soon thereafter suppressed, until 1992.
In 2002, the Ulaanbaatar mission was elevated to the present apostolic prefecture. The mission's superior, the late Fr. Wenceslao Padilla, a priest of the Immaculate Heart congregation, was appointed prefect, and was consecrated a bishop the following year. Padilla died in September 2018. Mongolia's first native priest was ordained in 2016.
Marengo told Vatican News in 2020 that because Mongolia's Catholic community is so small it is especially important to pay attention to interreligious dialogue and the cultural traditions of the Mongolian people.