Brother Antonius Mungsi O.Carm. is the son of Mr. Masudiharjo and Mrs. Lusia Rubunah. Brother Mungsi was born and raised in Sleman, Yogyakarta.

Brother Mungsi started living in the Wisma Shyanti Carmelite community in 1990 when he was studying at Cor Jesu Senior High School. After completing his study, he moved to Saint Elias Carmelite Monastery in Malang and then underwent his postulate at Stella Maris Postulate Malang. He entered the novitiate in 1993 and had his first profession in 1995.In 1999, he was assigned to continue his study at Sanata Dharma University in Yogyakarta. He was taking catechism. In 2002, he returned to Malang to prepare for his solemn profession. Later, he continued his studies in Yogyakarta and graduated in 2004. Upon his return from his study in Yogyakarta, he was assigned as a religious teacher at St. Paul Carmelite High School Jember. He worked as the pastoral care director.

In 2011, he moved to Malang and served as the director of Saint Albert boarding house. During that time he was also assigned to continue his study on education management at the State University of Malang. After completing his studies, he received an additional task to become the secretary of the Sancta Maria Foundation.