They were the first legally married interracial couple in Jackson, Mississippi, and Walker has said that although they were very much in love, she married him "because" it was illegal at that time in that state (they'd tied the knot back in New York). Threatened by the Ku Klux Klan, they slept with a gun under their bed.
That marriage ended in 1976 and, in the years since she's had a number of lovers, men and women. Through all the years of political activism she wrote when she could, and her first book, a poetry collection called Once, was published in 1976. Poetry, she still maintains, is the lifeblood of rebellion. "It's the quickest way of getting right to the intelligence and to the heart."
The Colour Purple - her most famous, defining work - was her third novel and, because of it, in 1983 she became the first African American woman to win the Pulitzer Prize for Fiction.
She's published many more books - novels, poetry, essays - and is, it's fair to say, a vibrant presence at the heart of black American literature and thought, and an influential voice on many political and humanitarian issues, from the American political system, to the Palestinian cause.
Her latest book, A Cushion In The Road, opens with a letter to Barack Obama on the eve of his presidency, expressing all the optimism and joy of a race whose slave ancestors built the White House, and who now saw one of their own about to walk in the front door. Yet, Walker says, Obama is a disappointment.
"I was very optimistic because he sounded really good. He made a lot of us feel like, at last, here's somebody with sense. But he is no longer that person. He belongs to the establishment, and it's a rotten establishment, and I don't see that we're going to get very far if we cling to it. The system is not only bigger than he is, it's so corrupt that he would be a magician if he survived and tried to buck it.
"He was a distraction," she concludes. "Just as Hillary Clinton will be a distraction if she becomes the first woman president. They pull these rabbits out of the hat and we fall for it every time, because we're so desperate."
As a child in the 1940s and 50s, Walker would sit with her family in the tiny, white-painted wooden church at Ward's Chapel just outside the town of Eatonton in Georgia. The minister spoke passionately about the Christian God of the Old and New Testaments, but Alice gazed out of the window - at majestic trees, the over-arching sky, the stretching landscape, and she felt how vast was the universe outside, and how small the church.
Until the age of 4 she was "babysat by nature", left to play at the edges of the cottonfields, watching her mother progress up and down the fields, while Walker crawled around, exploring and learning how alive was the natural world.
Later, in 1964, after she'd won a scholarship to Sarah Lawrence College in New York State, she came across a simple, Zen poem that gave her a moment of recognition, reconnecting her to her childhood experience of nature:
Sitting quietly,
doing nothing,
spring comes,
and the grass grows by itself.
It is this sense of nature, of connectedness, and the possibilities of meditative contemplation, that consistently shape her spirituality and her politics. "In day-to-day life, I worship the Earth as God - representing everything - and Nature as its spirit," she says.
She exhorts us to recognise that we have on our small, perfect planet everything we need to sustain us. Yet, she says, "it is crumbling beneath our feet ... Most of the humans on it are endangered, one way or another. I think people are deeply frightened and it has made a lot of them almost comatose."
She has no time or pity for those who feel there is nothing they can do to make a difference.
"I think they're lazy. And this is the problem. If you think 'I'm just little old me and I can't do anything about anything', well good, you go somewhere and you just stay in your cave. But for the rest of us we understand that we do have some power to live a decent life, a compassionate life, a life that pays attention to people rather than just brushes them aside. There's always something to do. You can change who you are and how you behave. If we don't change, we're done for."
The Colour Purple was published in 1982, an intensely political era when radical feminism and black separatism were potent ideas. The novel was widely seen as being uncompromisingly "about" the treatment of women by men, and the treatment of blacks in the southern states of America. Walker, though, has always said it's a theological novel.
"At the time, people missed that quality altogether," she says. "They never recognised what I'm doing in the book, which is really about God."
Which gets us back to that scene, of Walker in the church, staring out the window. Her God is an expansive god of trees, air, birds, people - an erotic god, even, who "love all them feelings", who "love everything you love". And God's messenger is none other than Shug, the sensual blues singer who awakens downtrodden Celie to her own strength, joy and sexuality. Celie eventually throws off the old God and embraces the new. Thus, was Walker exploring her own spirituality within the frame of that novel?
"Of course! Of course. Nature is my temple. It's all there is. I wanted very much to introduce that liberation into the culture because for most people there is just this straitjacket of organised religion, which ties people up worse than television."
Shot by a BB gun at age 8 and blind in one eye ever since, Walker struggled with the fear of blindness, and the bullying and isolation that came as a result of her disfigurement.
The thick white scar was later removed, but the memory of those painful years remained.
It taught her, she says, to see - to see beneath the surfaces of things, to understand that our bodies are simply containers for our spirits, and to listen beneath the surfaces of words to the intention of the speaker. All these qualities are evident in her lifetime of fearlessness, of facing up to what needs to be done.
"This life is rich beyond belief," she says. "There's just so much to think about and to do and to muse about and to wonder about and to enjoy and puzzle." She makes a tiny pause before adding: "And to act."
Alice Walker will appear at the Auckland Writers Festival, Aotea Centre, on May 18.
