But he's no darling of the "pro-choice" view, either, earning a score of 36 per cent once from NARAL Pro-Choice America for his votes on their select issues. Obama has a score of 100 per cent from NARAL.

Biden has also talked frankly about the importance of his faith in his life, maintains close ties with his Catholic high school and isn't hesitant to show off elements of his Catholic education in the Senate.

Biden was born in Scranton, Pa., and at age 10, the family moved to Delaware, where his father was a car salesman. He attended Archmere Academy, a Catholic prep school in Claymont, Del., but only after his mother told him he couldn't go into the seminary, as he wanted, until after he had some experience dating girls, his mother told a reporter in 2007.

He has maintained ties with Archmere, which sought to name a new student centre building for him in 2006. The plan was scrapped after Wilmington Bishop Michael A. Saltarelli opposed it, citing Biden's votes on abortion.

In a 2007 interview with the Christian Science Monitor, when he was a candidate for president himself, Biden said he grew up in the church at a time of great changes both in structure and in attitudes after the Second Vatican Council.

"I was raised at a time when the Catholic Church was fertile with new ideas and open discussion about some of the basic social teaching of the Catholic Church," Biden told the Monitor. "Questioning was not criticized; it was encouraged."

During the 1991 confirmation hearings for Supreme Court Justice Clarence Thomas, Biden, then chairman of the Senate Judiciary Committee, was the one who engaged Thomas in sometimes lengthy discussions about natural law and its application to civil law. The church' s teachings about issues such as the right to life of all human beings are based natural law, the philosophy that individuals have certain basic human rights that are based on universal moral principles or on "a higher law'' which is not limited by the letter of the law.

On issues including immigration, minimum wage, providing health care for all children and reinstating the assault weapons ban, his positions have been close to those of the church's lobbying efforts. Biden voted to authorize the invasion of Iraq in 2002, but later became a critic of the war.

Chris Korzen, executive director of Catholics United, a non-partisan organization that promotes the church's social justice message in the political arena, called Biden's selection a positive development. He said Biden's commitment to his Catholicism "has inspired his advocacy on issues such as genocide, universal health care, education, worker's rights and violence against women."

Korzen's statement said he's optimistic that Biden might "help move our nation beyond the divisive, acrimonious and unproductive debate" that has come to surround the issue of abortion. He noted that Biden has said he accepts the church's teaching that human life begins at conception and said Biden has a history of seeking practical ways of addressing abortion in ways that a broad spectrum of people can support.

Alexia Kelley, director of Catholics in Alliance for the Common Good, said Biden's "Catholic and working class roots have been a source of solidarity for him with hard-working American families who are suffering the most from the current economic crisis."