McCarrick, a leading moderate voice in the U.S. church, submitted his resignation as required of all bishops when he turned 75 in July. In a brief statement, the Vatican said Benedict had accepted McCarrick's resignation and named Wuerl to replace him.
"To follow in such large footprints requires an enormous amount of courage and support," Wuerl said at a news conference at Washington's Archdiocesan Pastoral Center in Hyattsville, Md. "While I am greatly aware that I have a lot to learn about this archdiocesan Church, I have strong ties to this community."
Wuerl spoke in both English and Spanish in recognition of the diversity among the 560,000 Roman Catholics in the archdiocese, which includes the District of Columbia and five counties in southern Maryland.
"We are absolutely delighted that the Holy Father gave us so special of a man," McCarrick said. "He's an extraordinary man, who you will love."
Wuerl, 65, who completed his ministerial training in Washington, is a native of Pittsburgh and returned to the city in 1988 after working in Seattle. He led Pittsburgh's Roman Catholic community of 800,000 for 18 years.
He was one of the American delegates at the Vatican's meeting of the world's bishops in October that tackled pressing issues facing the church, including a priest shortage. The bishops rejected any change to the celibacy requirement for priests and suggested dioceses share clergy and step up recruiting to cope with the shortage.
McCarrick has been in the spotlight in recent years as he tried to moderate the fierce debate over whether Catholic politicians must adhere to church teaching in their professional lives.
He headed a task force of the U.S. Conference of Catholic Bishops studying the issue and has said he didn't feel comfortable denying Communion to Catholic politicians who back abortion rights.
McCarrick has said that after stepping down he will divide his time between Catholic Relief Services and the Papal Foundation, a charity he helped establish.
Wuerl obtained a bachelor's degree in 1962 and a master's degree in 1963 from The Catholic University of America's Theological College.
He brings "a keen intellect, a profound sense of the spiritual, a clear focus on the Gospel and evangelization, and a deep love of and commitment to the church," the university's president, Rev. David M. O'Connell, said in a statement Tuesday.
In other appointments Tuesday, the Vatican said Benedict had named the bishop of Little Rock, Ark., Monsignor James Peter Sartain, to be bishop of Joliet, Ill.
Sartain, 53, replaces Bishop Joseph Imesch, who like McCarrick resigned because he will soon turn 75. While leading the diocese of 620,000 Catholics, Imesch came under criticism from victims' advocates for his handling of allegations of sexual abuse by priests.