During his time in Rome, Mueggenborg also became very involved with the Missionaries of Charity, which is how he met St. Teresa of Calcutta. Though it started as just a weekly commitment of one hour at their soup kitchen, his time volunteering with them eventually increased to much more.
After his ordination to the priesthood on June 14, 1989, he was asked to serve as a chaplain for their small convent at San Gregorio in Rome. Mother Teresa was present at three of the Masses that year, he wrote in the biography. After one of the Masses, she came to the sacristy and then joined Bishop-elect Mueggenborg and a classmate for breakfast.
"It was a remarkable experience to be in the presence of a woman who radiated the very presence of Christ," he said.
Bishop-elect Mueggenborg received a License in Biblical Theology in 1990 and returned to Tulsa. He served as parochial vicar and pastor at various parishes in the diocese, as well as chaplain of Bishop Kelly High School and Saint Philip Neri Newman Center at the University of Tulsa.
In 2005 he returned to Rome to serve as the Assistant Director of Formation at the Pontifical North American College, and then as Vice Rector of the college, from 2006-2011.
Since 2011 he has been pastor of Christ the King Parish in Tulsa, a member of the diocesan priests and financial councils and a member of the Board of Governors of the diocesan chapter of Caritas.
In addition to English, he speaks Spanish and Italian.
He is the second priest from the Diocese of Tulsa and Eastern Oklahoma to be appointed bishop recently, after Oklahoma native Msgr. Peter Wells was made a bishop in 2016, Bishop David A. Konderla of Tulsa wrote in a statement on the diocese's website.
"These appointments are a great statement of confidence from the Holy Father for the Church in Eastern Oklahoma, and the appointment of Msgr. Mueggenborg will only strengthen our communion with the universal Church," he said.
"We congratulate Msgr. Mueggenborg on his appointment and knowing we will miss him, we wish him a fruitful ministry in the Archdiocese of Seattle."