Doris Derby has had a productive 81 years. She’s been an elementary-school teacher, a photographer and a civil rights activist. She has founded theatre groups and been a professor of anthropology. “I like to say, I’ve worn a lot of different hats,” she tells me with a laugh one morning last week on the phone from her home in Atlanta, Georgia.

Today we are mainly talking about her photographs, a selection of which are to feature in a new exhibition at Turner Contemporary in Margate called We Will Walk – Art and Resistance in the American South. But the story behind Derby’s wonderful, intimate pictures is enmeshed with the rest of her extraordinary life; she often wore several of her hats at the same time. Her experience also provides a revealing snapshot of the rupture that America went through in the 1960s and 70s.

Derby grew up in the Bronx, New York, and an engagement with the civil rights movement was in her DNA: her grandmother was an early activist in the NAACP (the National Association for the Advancement of Colored People); her father was a civil engineer often overlooked for jobs he was well qualified for. “When I was in elementary school, nothing in the history books had anything to do with telling me about my history,” she says. “I’d think: ‘Why aren’t black people being represented in these books? And stories, movies.’ We weren’t in them. But we were here.”

Schoolchildren, Farish Street, Jackson, Mississippi, 1968. Photograph: © Doris A Derby

But Derby became fully committed in 1963: the year of landmark protests in Birmingham, Alabama, and the March on Washington (where Martin Luther King Jr told the 250,000-strong crowd: “I have a dream”). She’d been asked to work on a literacy programme in Mississippi – initially she said no, but events demanded a rethink. “As many other people were, I was aghast at what was happening in Birmingham,” Derby remembers, “with the police and their dogs and the firehoses and the billy clubs, beating these people who are dressed up orderly, and just trying to see about integrating the facilities there, and seeing about registering to vote. I saw that on the news, and I just decided that if these people were so brave to do that, to fight for the right to vote for all of us as black people, then the least I could do would be to go to Mississippi to work.”

Initially, Derby was involved with teaching and voter registration, but around 1966 she was given a camera by a new organisation, Southern Media, which was setting out to document the civil rights movement. While many of the most famous images from this period show violent confrontations, protests and the iconic leaders, Derby’s approach was different. She was especially interested in women and children, and the day-to-day experience of life in the south at that time. Her photographs didn’t appear on the front pages of newspapers, but were instead used on brochures and leaflets that were distributed directly to the black communities, showing the activities and initiatives that were a less showy but still essential part of the civil rights changes.

Derby’s father had given her a Brownie camera when she was a child, and she had an instinctive eye for detail and storytelling. “I also was a painter before I came to Mississippi,” she says, “so a lot of my pictures, when I look through the lens, I’m looking also from a perspective of: ‘How would this look as a picture, a painting?’”

A women’s sewing co-operative, Mississippi, 1968. Photograph: Copyright Doris A Derby

Although Derby was not usually at the frontline of protests, there was an ever-present risk in her work. “I had threats around me, I had situations,” she says matter-of-factly. Derby recalls visiting black farmers and the men would stay up all night, guns at their side. “They were very brave,” she says. “Especially in the rural areas, they were threatened that if they had anything to do with the civil rights movement, they would be thrown off the land. There could be firebombs shot into their houses and I knew people that happened to.”

Another time, Derby went into a gas station to use the bathroom. “This was a time when civil rights people were integrating bathrooms and other facilities,” she explains. “And a guy came over to me and he put his hand on his waist and he had a gun there. And he told me which bathroom I’d better use.” What did Derby do? “I just left,” she goes on. “I didn’t go in the bathroom. But I mean, he was prepared to do things. So you never knew when things were going to happen.”

Derby insists that it was not particularly unusual for a woman to chose to move to the south, with all the dangers that entailed. What was rare in her case, though, was how long she stayed: nine years, until 1972, when she went to the University of Illinois to study anthropology. “I was just…” she pauses. “I was very involved in the work in Mississippi. I felt like it was what I should do. And it just seemed like more things came up that could use my skills and it was just my time to give what talent I had. There was such a need, and my skills were needed.”

• We Will Walk – Art and Resistance in the American South runs at Turner Contemporary, Margate, 7 February-3 May