Paul McCartney was born in Liverpool, England.
His mother was a Roman Catholic and Paul was baptized into that church. Paul's father was a Protestant, but Paul asserts that he was raised largely without religion.
The Beatles, and Paul McCartney, went through a series of religious/spiritual phases. In a widely-publicized event in 1968, all four Beatles studied under the Hindu guru Maharishi Mahesh. But the religion didn't seem to stick with any of them except George Harrison.
During some interviews, Paul hinted at agnosticism/atheism, saying:
We probably seem anti-religious because of the fact that none of us believe in God… We're all agnostics.
As time wore on, Paul grew up and Beatlemania subsided enough for the four members to get on with their lives and contemplate the cosmos in quiet. Paul softened his views on religion.
I'm not religious, but I'm very spiritual.
McCartney referenced God in a song called "Freedom," which was in honor of 9/11 victims, saying that:
This is my right, a right given by God. To live a free life, to live in freedom.
Still, McCartney hasn't truly come around to religion yet, despite rumors of converting to Judaism for his most recent wife, Nancy Shevell.
Activism, not politics
McCartney has actively taken up quite a few causes in his long career as mega-celebrity.
Most, though not all, of McCartney's activism has centered around animal rights. He explained the genesis of this choice to dedicate his considerable star power to animals, saying:
Many years ago, I was fishing, and as I was reeling in the poor fish, I realized, 'I am killing him – all for the passing pleasure it brings me'. Something inside me clicked. I realized as I watched him fight for breath that his life was as important to him as mine is to me.
His activism has included fighting for the preservation of seals, criticizing the Chinese government and boycotting the 2008 Beijing Olympics over their fur industry, and writing a letter to the Dalai Llama, urging him to be a vegetarian.
In terms of U.S. politics, McCartney has been a supporter of Obama and has slammed Bush, saying:
It's nice to have a president who knows what a library is.
Though he's British, so we can't call him a Democrat, he's an Obama supporter and an animal rights activist, so he's a liberal in our eyes.