Bui was ordained during a Mass celebrated by Bishop John Dolan before nearly 2,500 worshippers, including clergy, seminarians, diocesan officials, dignitaries and laity at St. Thomas Aquinas Church in Avondale, Ariz. There were more than 20 bishops and cardinals, over 200 priests and over 80 religious in attendance.
Bishop Dolan led the prayers of consecration, assisted by Auxiliary Bishop Eduardo Nevares and Bishop Emeritus Thomas Olmsted, marking an historic moment as all four diocesan bishops took part in the same ceremony.
Bui was appointed Dec. 19, 2025, by Pope Leo XIV.
“Today the Diocese of Phoenix rejoices with deep gratitude,” Bishop Dolan said in his homily.
“Our Holy Father has chosen a wonderful shepherd. One formed by missionary service, refined by pastoral love and marked by the heart of Christ Himself. Peter comes to us with amazing, extraordinary and beautiful credentials.”
Ordained to the priesthood Dec. 24, 2003, Bui brings a diverse background to his new role, including service as a Legionaries of Christ missionary in South America, leading or assisting pastors at four parishes in the diocese and six years at the Vatican as an official with the Pontifical Council Cor Unum, which leads the Church’s charitable, humanitarian and disaster-relief work around the world. During that time, in 2014, Pope Francis gave him the title of monsignor.
Fluent in Spanish, German, Italian, English and Vietnamese, Bui studied philosophy and theology at the Pontifical Athenaeum Regina Apostolorum in Rome.
Bui was named by then Bishop Olmsted as the diocese’s Vicar for Clergy in 2022, a post he will continue as auxiliary bishop.
Bui’s early life was marked by the perils of his country falling to Communism.
Following the Vietnam War and the surrender of South Vietnam to the Communist North, Bui’s parents decided to leave their home on Phu Quoc Island on the far southwestern tip of Vietnam, fleeing in the middle of the night in Bui’s father’s packed commercial fishing boat. Under the cover of darkness, Bui’s siblings, parents and nearly three dozen neighbors and friends ventured out into the Gulf of Thailand on a perilous five-day voyage marked by a robbery at gunpoint by pirates before reaching the coast north of Bangkok and an eventual flight to the United States.
Bishop Dolan said this experience, as well as the years that followed growing up in New Orleans, instilled within Bui an ability to carry out his duties with love — today’s overarching Church mandate.
“He knows what it means to be a refugee … searching for safety and hope,” said Bishop Dolan. “He knows what it means to arrive in a new land; to depend on the kindness of strangers and discover the providence of God in a new home.”
In New Orleans, Bui also learned how to value the individual, the bishop continued, using a popular phrase of the city: “Who dat?”
“‘Who dat?’ At its heart, it’s a chant of belonging. It means, ‘we know who we are, we stand together, we don’t face the world alone.’”
Cardinal Christophe Pierre, the Vatican’s Apostolic Nuncio to the United States, who presented Bui with the signed papal document of his appointment, said the new auxiliary bishop’s life and service formed him in a Church that is truly universal yet always attentive to the complete needs of God’s people.
“As an auxiliary bishop, your ministry will be one of closeness, walking with people. Remember, unity is not uniformity but communal, rooted in Christ. As the Holy Father likes to say, ‘In the One, we are one,’” Cardinal Pierre said in his thick French accent.
Following the Rite of Ordination, during which Bui lay prostrate before the altar, with bishops Dolan, Nevares and Olmsted leading the congregation in prayer to the great saints of the Church, Bui was presented three symbols of his new office: his ring, reflecting his spousal love for and fidelity to the Church and especially for the diocese; his miter, the headdress signifying his authority and function; and his crosier, the shepherd’s crook-shaped staff reflecting the pastoral care and duty entrusted to him.
Later, following Communion at the closing of the Mass, Bui spoke publicly for the first time in his new role, first thanking his brother priests.
“St. John Vianney taught us the priesthood is the heart of Jesus. For three and a half years as Vicar for Clergy, I have witnessed that love in your ministry. When you radiate His love, mercy and compassion, God’s people truly encounter the living Christ,” he said.
He then reflected on the fact that Ash Wednesday, the start of Lent, would begin in less than 24 hours.
“What better way to begin an episcopal ministry than by entering into Lent together with all of you,” Bui said. “It’s the perfect reminder that this sacred office isn’t about me. It’s about serving Christ and His people with a humble heart.
“To all the faithful of the Diocese of Phoenix,” he continued, “you have shaped me through prayers, your faith and your example of Christlike love. Please keep me in your prayers.”
Though his father and one sister are no longer living, Bui said, “I truly felt their presence today.”
He thanked his mother, 89, who he said still prays the Divine Mercy chaplet daily.
“Her faithfulness to prayer is the very foundation beneath everything I do. Thank you for teaching me [to] pray; to trust in God’s mercy and to never give up.”
To his living brothers and sisters in attendance, he recalled, “growing up as one of 12 children was chaotic, loud, but absolutely wonderful. You taught me how to share, how to serve, how to laugh at myself and how to love. I wouldn’t be here without you. Thank you for being my first community, my first teachers in what it means to live together in love.”
Thahn, Bui’s youngest brother, recalled that while shocked at first when he learned of Bui’s appointment, it ultimately wasn’t surprising.
“I knew he had a call, the way he handled himself when he was little. I looked up to him,” he said.
Kim, his oldest sister, called it a touching ceremony.
“There was a lot of love and joy. [His] was an incredible journey; an incredible story.”
As auxiliary bishop, he joins Bishop Nevares in assisting Bishop Dolan as shepherd of a culturally and ethnically diverse diocese of over 2 million Catholics, one of the fastest growing in the United States. According to The Official Catholic Directory, a reference resource published yearly by the U.S. Conference of Catholic Bishops, Phoenix is now the nation’s second-largest diocese by Catholic population, exceeded only by the Archdiocese of Los Angeles, which is home to over 3.79 million faithful and six auxiliary bishops.
In the past decade alone, more than half a million individuals have joined the diocese, either by moving or completing the Order of Christian Initiation of Adults. A record 50-plus seminarians are now in various formation stages at Nazareth Seminary, the diocese’s local seminary.
“As one of the largest and most rapidly growing dioceses in the nation, Phoenix faces increasing pastoral and administrative complexity…” Bishop Dolan stated the day Bui’s appointment was announced. “Bishop (-elect) Bui’s experience in governance, his deep care for priests and his commitment to accompaniment will be invaluable.”
The ordination and the surrounding celebrations are made possible through the generous support of Clint and Jennifer Hickman; Dr. Kenneth and Angeline Osorio; The Diane and Bruce Halle Foundation; Catholic Cemeteries and Funeral Homes; Catholic Education Arizona; Notre Dame Federal Credit Union; AllThrive365; Catholic Charities Community Services; The Society of St. Vincent de Paul; and Catholic Community Foundation. With grateful hearts, we thank these benefactors for their faithful generosity and partnership in supporting the life and mission of the Church.