O'Brien has frequently appeared in the press, including writing opinion pieces in The Baltimore Sun, to make the Church's position known: opposing the death penalty, arguing for humane immigration practices, and advocating for the continued religious ownership of St. Joseph Medical Center in Towson, among other issues.
He testified in Annapolis in support of tax credits to aid Catholic schools and filed a federal lawsuit to try to block a Baltimore law that requires pregnancy counseling centers to post signs stating that they do not refer women for abortions or birth control. The law was voided by a federal judge last year, and the ruling is being appealed.
O'Brien has put the Catholic Church's positions at the forefront of political debate in Maryland even as his time here is winding down. This month, O'Brien said in a strongly worded letter that the archdiocese would not submit to a federal law that required religiously affiliated institutions to offer birth control coverage, even it means dropping health insurance for its 3,500 employees.
"We cannot — we will not — comply with this unjust law," O'Brien wrote in the letter, which was read during Sunday Mass at the area's 153 Roman Catholic parishes. The Department of Health and Human Services regulation was later revised to require insurance companies to make birth control available at no cost to religious employers that object to contraception.
Then, on Thursday, O'Brien called from Rome to speak with state delegates to persuade them to vote against O'Malley's Civil Marriage Protection Act.
About halfway through his stint in Baltimore, O'Brien confronted one of his most difficult issues. In the face of rising costs and declining enrollment, the Baltimore Archdiocese decided in March 2010 to close 13 schools, including Cardinal Gibbons in Morrell Park, a storied West Baltimore high school. The move displaced more than 2,000 students.
"The archbishop really didn't have a choice in the matter," Schuster said Friday, reflecting on his interactions with O'Brien after the closure announcement. Schuster vigorously opposed the closures, and went so far as to buy radio ads telling Catholics not to make donations to their parish's collection plate on Easter Sunday.
Schuster offered the archdiocese $700,000 in order to continue the operation of some of the schools, an offer O'Brien declined. But the two men arrived at a compromise: Busing students to nearby Catholic schools that remained open.
Schuster, who said he is paying about half the cost of the busing program, is pleased with the result. Roughly a quarter of the students at closed schools continued at Catholic institutions by using the bus program.
Though their relationship started off tense, Schuster came to appreciate O'Brien's leadership. He has since promoted the busing program in radio ads.
Jay Dillow, who said his family has generations of history with Baltimore's Catholic school system, was left with a different feeling about O'Brien's leadership style after the closure of Cardinal Gibbons.
"I drive by the building weekly … and seeing the facility not being used is tough," said Dillow, who launched a small nonprofit after hearing that the school was slated to be closed. He and other Gibbons boosters gathered funds to preserve the school's history and offer scholarships, and one day they hope to reopen the building.
Dillow said O'Brien didn't meet with his group. When Dillow met with archdiocese staffers about the Gibbons closure, he said: "We were just told the archbishop said so and that's how it was going to be."
Even now, almost two years since the closure, the archdiocese has been tight-lipped about the future of the Gibbons property.
The way it was handled "causes people to question that faith and belief structure," Dillow said of Gibbons' closure. As a result, he said, he sees fewer people in the pews on Sunday.
Dillow's main hope for O'Brien's successor is a willingness to engage in open dialogue with members of the archdiocese.