[2] Lucas was raised by the Vatican to the rank of honorary prelate on September 5, 1994, and appointed by the archbishop as vicar general of St. Louis for a year before becoming rector of Kenrick-Glennon Seminary in 1995.

On October 19, 1999, Lucas was appointed the eighth bishop of the Diocese of Springfield in Illinois by Pope John Paul II.

He received his episcopal consecration on December 14, 1999, at the Cathedral of the Immaculate Conception in Springfield, from Cardinal Francis George, with Archbishop Gabriel Higuera and Bishop Daniel L. Ryan serving as co-consecrators.

[5] The same allegations were raised again in 2021 in a lawsuit by Anthony J. Gorgia, a former seminarian, against the Pontifical North American College in Rome and the Archdiocese of New York.

[5] In July 2004, Lucas approved a $1.2 million settlement to eight men who had been sexually abused as minors by Walter Weerts, a diocese priest at Sacred Heart Parish in Villa Grove, Illinois between 1973 and 1980.

[6] Lucas spearheaded the Built in Faith campaign to raise the $11 million needed to restore the Cathedral of the Immaculate Conception.

[4] Within the United States Conference of Catholic Bishops, Lucas sits on the Subcommittee on the Catechism and Sapientia Christiana Committee.

[7][failed verification] He received the pallium, a vestment worn by metropolitan bishops, from Benedict XVI on June 29, 2009, in a ceremony at St. Peter's Basilica in Rome.

[8] In October 2010, Lucas suppressed Intercessors of the Lamb, a hermit religious community, removing it from any association with the Catholic Church.

[12] In October 2018, Lucas removed Francis Nigli, pastor of St. Wenceslas Parish in Omaha, from public ministry due to inappropriate sexual advances to an adult.

[14] On July 31, 2024, Lucas announced that he gave his resignation to Pope Francis on June 12, 2024, as normally required when a bishop turns 75 years old, insisted he stay on until a successor is named.

[15] Pope Francis appointed Lucas to also serve as the apostolic administrator of the Diocese of Lincoln on December 13, 2019, when Bishop James D. Conley took a temporary leave of absence.