The son of the country's most famous Catholic family defied church teachings when he divorced his first wife, then was granted an annulment only after he admitted he wasn't being honest when he promised her he'd be faithful. His most significant and public break with the church came with his support for abortion rights.
Yet Kennedy also advocated for signature Catholic causes, such as help for the poor, health care and immigration reform, and opposition to the Iraq war. His faith remained a regular part of his life until it ended this week with a priest at his bedside.
The apparently conflicting portrait of a man loyal to the church despite widening disagreement on key issues "almost perfectly represents" the views of most American Catholics, said Boston College professor Alan Wolfe.
"He's an effect of a process that's been going on for a very long time that started long before Teddy Kennedy was born and will continue long after Teddy Kennedy is dead," Wolfe said.
Kennedy's mother, Rose Kennedy, set the roots of his faith, emphasizing Christ's teaching in the Gospels that "to whom much is given, much will be required." When her kids were teens, she made sure they went to a weekend religious camp every year, even if they'd rather be sailing, said Adam Clymer, who worked with Kennedy on his biography. She took them to church during the week, so they knew church wasn't just for Sundays.
In his eulogy during her 1995 funeral, Kennedy called his mother's faith "the greatest gift she gave us."
A commitment to Catholicism was not always evident in Kennedy's personal life, which was marred by problems with alcohol and philandering. In 1983, he was forbidden from receiving communion after his divorce - which the church forbids - from his first wife, Joan.
The public learned more than a decade later that he'd been granted an annulment after he was seen accepting Communion at his mother's funeral. Joan later said that Kennedy requested the annulment, which she did not oppose, on grounds that his marriage vow to be faithful had not been honestly made, Clymer said.
Kennedy never discussed his annulment and also rarely spoke publicly of his Catholicism.
"I think faith oftentimes is deeply felt in the marrow of your bones, it's a matter of the heart," said Kennedy's friend, the Rev. Gerry Creedon, a Washington-area priest. "He had trouble articulating his inner feelings, his deepest conviction and matters of emotion, the heart."
One of Kennedy's longest discussions of his faith came in 1983 in an unlikely place - political foe Jerry Falwell's Liberty University:
"I am an American and a Catholic; I love my country and treasure my faith," Kennedy said. "But I do not assume that my conception of patriotism or policy is invariably correct, or that my convictions about religion should command any greater respect than any other faith in this pluralistic society. I believe there surely is such a thing as truth, but who among us can claim a monopoly on it?"
In the same speech, Kennedy referred to abortion, criticizing some religious people for wanting government to "tell citizens how to live uniquely personal parts of their lives." His pro-abortion rights stance was a flip from early in his career and tough for many Catholics to accept, even those who admire his work in other areas they consider "pro-life" - such as anti-war, anti-poverty and anti-death penalty causes.
"There's this big, 'What if?'" said Catholic author Michael Sean Winters. "If Ted Kennedy had stuck to his pro-life position, would both the (Democratic) party and the country have embraced the abortion on demand policies that we have now? And I don't think so."
Read more stories on Sen. Kennedy's life and death at CBSNews.com:
Russell Shaw, former spokesman for the U.S. Conference of Catholic Bishops, said when Kennedy defied the church on issues such as abortion and later, gay marriage, he reinforced a corrosive belief among Catholics that they can simply ignore teachings they don't agree with.
Kennedy's differences with the church never kept him from Mass. When he was in Washington, Kennedy would attend Blessed Sacrament Church in Chevy Chase, Maryland, and sometimes stop in at St. Joseph's on Capitol Hill, said Susan Gibbs, spokeswoman for the Washington Archdiocese. In his last days, Kennedy leaned hard on his faith. Creedon said he visited with Kennedy last Friday, offering him a blessing and praying the Lord's Prayer with him.
"He just was a man of deep piety and devotion, as well as public commitments in the area of the Gospel," Creedon said.
Kennedy's relationship with the Catholic church was rocky, Shaw said, but there's no doubt it was enduring. Judging the quality of Kennedy's faith isn't for him, he said.
"Now it's up to God," he said.
By Associated Press Writer Jay Lindsay