When they were children, Memory Banda and her younger sister were inseparable, just a year apart in age and often mistaken for twins. They shared not only clothes and shoes, but also many of the same dreams and aspirations.

Then, one afternoon in 2009, that close relationship shattered when Ms. Banda’s sister, at age 11, was forced to wed a man in his 30s who had impregnated her.

“She became a different person then,” Ms. Banda recalled. “We never played together anymore because she was now ‘older’ than me. I felt like I lost my best friend.”

Her sister’s pregnancy and forced marriage happened soon after her return from a so-called initiation camp.

In parts of rural Malawi, parents and guardians often send their daughters to these camps when they reach puberty, which Memory’s younger sister hit before she did. The girls stay at the camps for weeks at a time where they learn about motherhood and sex — or, more specifically, how to sexually please a man.

After her sister’s marriage, it dawned on Memory that she would be next, along with many of her peers in the village.

Strong feelings of resistance, she said, began stirring within her.

“I had so many questions,” she said, “like, ‘Why should this be happening to girls so young in the name of carrying on tradition?’”

It was a moment of awakening for the self-described “fierce child rights activist,” who, now 27, helped in a campaign that, in 2015, led Malawi to outlaw child marriage.

Despite the passage of the law against child marriage, enforcement has been weak, and it is still common for girls here to marry young. In Malawi, 37.7 percent of girls are married before the age of 18 and seven percent are married before turning 15, according to a 2021 report from the country’s National Statistical Office.

The drivers of child marriage are multifaceted; poverty and cultural practices — including the longstanding tradition of initiation camps — are important components of the problem. When girls return from the camps, many drop out of school and quickly fall into the trap of early marriage.

In the past, almost every girl in certain rural areas of the country went to initiation camps, said Eunice M’biya, a lecturer in social history at the University of Malawi. “But this trend is slowly shifting in favor of formal education,” Ms. M’biya said.

Ms. Banda’s own grassroots activism began in 2010, when she was just 13, in her small village of Chitera in the district of Chiradzulu, in Malawi’s south.

Despite initial resistance from older women in her village, she rallied other girls in Chitera and became a leader in the local movement of girls saying no to the camps.

Her activism gained momentum when she crossed paths with the Girls Empowerment Network, a Malawi-based nonprofit that was lobbying lawmakers to address the issue of child marriage. It was also training girls in the Chiradzulu District to become advocates and urge their village chiefs to take a stance by enacting local ordinances to protect adolescent girls from early marriage and harmful sexual initiation practices.

Ms. Banda teamed up with the nonprofit on the “I will marry when I want” campaign, calling for the legal marriage age to be increased to 18 from 15. Other rights activists, parliamentarians, and religious and civil society leaders joined the ultimately successful battle.

Today, the Malawi Constitution defines any person below age 18 as a child.

Ms. Banda’s role in the push against the practice earned her a Young Activist award from the United Nations in 2019.

“Our campaign was very impactful because we brought together girls who told their stories through lived experience,” Ms. Banda said. “From there, a lot of people just wanted to be part of the movement and change things after hearing the depressing stories from the girls.”

Habiba Osman, a lawyer and prominent gender-right advocate who has known Ms. Banda since she was 13, describes her as a trailblazer. “She played a very crucial role in mobilizing girls in her community, because she knew that girls her age needed to be in school,” she said. “What I like about Memory is that years later, after the enactment of the law, she’s still campaigning for the effective implementation of it.”

In 2019, with the support of the Freedom Fund, an international nonprofit dedicated to ending modern slavery, Ms. Banda founded Foundation for Girls Leadership to promote children’s rights and teach leadership skills to girls.

“I want children to understand about their rights while they are still young,” Ms. Banda said. “If we want to shape a better future, this is a group to target.”

Though her nonprofit is still in its infancy, it has already managed to help over 500 girls faced with child marriages to avoid that fate and stay in school or enroll again.

Last year she shared what she has been doing with Michelle Obama, Melinda French Gates and Amal Clooney during their visit to Malawi as part of the Clooney Foundation for Justice’s efforts to end child marriage.

“I’ve watched these three inspiring women from a world apart and just to be in their presence and talk to them was such a huge moment in my life,” Ms. Banda said. “I never thought I’d one day meet Michelle Obama.”

Ms. Banda was born in 1997 in Chitera. Her father died when she was 3, leaving her mother to raise two infant girls on her own.

Ms. Banda did well in school, knowing from an early age, she said, that learning was crucial for her future.

“My sister’s experience fueled the burning desire I had for education,” she said. “Whenever I was not in the first position in my class, I had to make sure that I had to be No. 1 in the next school term.”

Outspoken in class, her willingness to ask questions and express herself proved essential when her time came to go to the initiation camp. She refused.

“I simply said no because I knew what I wanted in life, and that was getting an education,” she said.

The women in Chitera labeled her as stubborn and disrespectful of their cultural values. She said she often heard comments like: “Look at you, you’re all grown up. Your little sister has a baby, what about you?” Ms. Banda recalled. “That was what I was dealing with every day. It was not easy.”

She found support from her teacher at primary school and from people at the Girls Empowerment Network. They helped convince her mother and aunts that she needed to be allowed to make her own decision.

“I was lucky,” Ms. Banda said. “I believe if the Girls Empowerment Network had come earlier in my community, things would have turned out different for my sister, as for my cousins, friends and many girls.”

Ms. Banda stayed in school, earning an undergraduate degree in development studies. She recently completed her master’s degree in project management.

She now works in Ntcheu, Malawi, with Save the Children International while running her own children’s rights nonprofit in Lilongwe. Malawi’s capital.

As much as she has accomplished, Ms. Banda is aware there is much left to do.

“Some of the girls that we have managed to pull out of early marriage, ended up getting back into those marriages because of poverty,” Ms. Banda said. “They have no financial support, and their parents cannot take care of them when they return home.”

She noted that child marriage is a multidimensional problem that requires a multidimensional solution of scholarships, economic opportunities, child protection structures at the community level and “changing the way families and communities view the problems,” she said.

Ms. Banda is currently lobbying Malawi’s Ministry of Gender to set up a “girls fund” to help provide economic opportunities to those most vulnerable to a childhood marriage.

For her sister, the first, forced marriage didn’t last. While now remarried to a man she chose as an adult, her childhood trauma disrupted her education and ended her ambitions of becoming a teacher.

Ms. Banda’s next move is to set up a vocational school for girls through her nonprofit, aimed at providing job skills to those like her sister unable to go beyond secondary school.

“All I want is for girls to live in an equal and safe society,” she said. “Is that too much to ask?”