Speakers - including the UK prime minister David Cameron, girls education champion Malala Yousafzai and actress Freida Pinto - were part of a packed day, which brought together campaigners, policymakers and development professionals, from around the world, to a school in south London.
The Girl Summit captured imaginations beyond the hall, however, with a public pledge to end FGM and child marriage reaching a staggering 700 million people through social media.
We were here for the historic day, communicating the key moments as they happened, plus our own reactions. Read from the bottom up to get the full run down.
17:30 - Farwa, a young girl from Pakistan, ended the day with an inspiring speech that definitely makes it clear that the Girl Summit is the start of something big: "I'm fighting to end child marriage and end FGM. Now it's your turn - what are YOU going to do?"
17:15 - Just announced by Nick Clegg: more than 300 faith leaders in the UK, from all faiths, have signed a declaration condemning FGM.
17:05 - UK deputy prime minister Nick Clegg's closing remarks are well worth sharing with the world: "We're here because, every day, millions of girls and women all over the world find their voices silenced simply because of their gender. For thousands of years, those in power and influence have turned a blind eye to those in pain and the activists who've found the courage to speak out. That conspiracy of silence is finally broken."
>> Just over a year ago, Nick Clegg wrote this piece for Girl Effect, explaining exactly why girls' rights are a priority for him.
"Together we can change things - and I'm grateful to each of you who have shown your support today. These practices are not confined to the developing world. They impact every single one of us and no country can afford to ignore them. Every year, around 60,000 girls at risk of being cut. This fact should infuriate every Briton. So, today's summit is about all of us: governments, NGOs, activists, faith groups, businesses like Nike, community leaders, the media, wider public and people affected by these practices - saying enough is enough. Together we can kick start a global movement to end FGM and forced marriage once and for all, wherever they occur. And it will take all of us - men, women, boys and girls."
>> Read Nick Clegg's Girl Summit closing speech in full, including his objectives, goverment announcements and conclusion.
16:54 - Maria Eitel is standing up and telling Girl Summit all about what it means to her: "There's a magical moment that's happened here. All the organisations in this room and the journey have worked for years to get here. What I'm afraid of is we see the summit as a destination. This is a starting point. The thing that has struck me most, and if I could pick one word, it's energy. We need to build on that energy. I've talked to thousands of girls around the world and they always say the same thing: don't just talk, give us action. So we have to deliver for them."
16:52 - Playing now on screen? The incredible Girl Effect Live film which features girls answering what their one wish for girls in poverty is - and it's looking great.
16:46 - Freida Pinto starts with a powerful, shocking statistic: "Every 10 seconds some girl in Africa is cut."
>> Read Freida Pinto's exclusive interview with Marie Claire, on why right now is the time to galvanise efforts and keep talking in order to end FGM and forced child marriage in a generation.
16:30 - Fantastic quote from Justine Greening: "This is the beginning, not the end of the process. After today, let's keep the spotlight firmly on these issues. Let's keep up the momentum, keep up with these promises. We need to make sure that there is a standalone gender goal, that includes specific targets around ending child marriage and ending FGM."
>> To make sure we do keep this momentum going for the next set of global development targets, we spoke to girls from all over the world and created the Girl Declaration.
16:24 - Justine Greening just announced investment of £25m to reach six million girls in Africa, Asia and the Middle East, plus £31m in a new research programme.
16:21 - A Girl Summit in Ghana will happen - and we're all invited. The agenda of ending early and forced marriage and FGM will be pushed forward from West Africa.
16:14 - Norweigan government just pledged to double investment in education over the next three years, with a particular focus on girls.
15:57 - Integrate Bristol are playing their #UseYourHead music video - audience are loving it.
>> One of Integrate Bristol's volunteers Fahma Mohamed inspired the UK government to take action against FGM. She told us how - and why - in a piece we published last month.
15:55 - Girls know best what girls need. That's what we're hearing during the Youth for Change panel: "Work in partnership with us youth and support our campaigns."
15:47 - Executive director of UN women Phumzile Mlambo-Ngcuka has just announced what's going to be at the core of the Youth Panel discussion: that FGM and child marriage are a result of gender inequality.
15:43 - Justine Greening is stressing that the Girl Summit is about youth. Just in time for Plan's Youth Panel, starting now.
>> There are a lot of promises being made today. Make sure you catch up with ALL the Girl Summit commitments that have been made so far.
15:36 - Japan intends to implement three billion yen over three years, through support to Unicef, the United Nations Population Fund (UNFPA) and others, to achieve gender equality.
15:34 EU commits 100 million euros to the causes of ending child marriage and FGM.
15:33 - Representative from Egypt now talking: "We are committed to promoting girls' education and to influence others to do the same. It's time to make sustained efforts on the ground. Our commitments extend to working with everyone, especially youth, girls and women. We are committed to having a good basis of data and research, coupled with a good monitoring system, to end FGM for good."
15:21 - Sweden's minister for international development Hillevi Engström has announced their support in the form of $350m for girls in Africa. The key area for the strategy is preventing child marriage and sexual violence and violence against girls and women - including, of course, FGM.
15:10 - Session two is just starting: time for quick-fire commitments and pledges.
14:25 - Social scientist Dr Annabel Erulkar is speaking in the first session of the afternoon. During 'Experiences in scaling up community social change', she's just touched on the work of Berhane Hewan.
12:50 - Closing remarks from David Cameron sum up everything we believe: "What this has got to be about is building a global movement. To check we don't just change the law, we change the culture. To check that we follow up on the commitments made. Now let us take this campaign, let us run it globally, let us outlaw these practices and let us change the state of our world."
>> Read how Rwanda's first teen magazine Ni Nyampinga is making changes for girls in Rwanda: "It's helped inspire them, and girls now know the future is in their own hands. I think in 10 years girls will be able to live their own independent lives, and know they are equal with boys.
12:47 - David Cameron: "In the past, we've been rather coy about advertising in schools about what needs to change, and worried about upsetting people's cultural sensitivities. That's changed. We have a forced marriage unit in the foreign office. We also now have advertising campaigns and school campaigns so that young people can see what their rights are."
>> One of the main issues under discussion around FGM is the summer holiday 'cutting season', known to be a particularly dangerous time for at-risk girls.
12:46 - Question time: First one is... how are you going about creating awareness in schools? David Cameron has just been passed a DVD on this very subject.
12:45 - David Cameron: "We'll follow up on every commitment made. This is about the world that we want our children to grow up in. Instead of just signing agreements, just passing laws, we actually commit to doing everything we can to outlaw these practices globally. That is the commitment that we have made. That is the commitment that all these countries have made."
12:40 - David Cameron: "These practices are a violation of girls' rights. They are a total violation of a chance to enjoy your childhood and a chance to have a fulfilling life."
12:15 - Malala's just blown the audience away with this speech: "It's the duty of every person, boy or girl, to get education and to get knowledge. We are human beings and we make the traditions. We make culture and we have the right to change it. A girl is a human being and she should be respected. A girl has the right to be treated as a boy. A boy has the right to live his life how he wants. A girl needs to have that too - to choose who she marries and what she does with her life. The solution is educate the girl. Let's make her independent. When a girl gets educated she can be independent. Education is the best way to fight all of the problems we are discussing right now."
12:09 - High-level session in session: prime minister of Bangladesh Sheikh Hasina, first lady of Burkina Faso Chantal Compaore, and Malala Yousafzai are discussing child marriage.
11:48 - The incredible (and first ever Insta-documentary) FreedomIs film just played for everyone here.
>> Watch the Girl Summit FreedomIs film and sign the Girl Summit pledge.
10:46 - Malala's father takes to the stage with a fantastic opening line: "#Malala used to be my daughter, but now I am her father."
10:30 - Malala has just arrived
>> Malala's one of our long-time girl heroes. Wanna know why? Check this out.
10:30 - Girls Not Brides' Mabel van Oranje is talking: "We need to work together. No one can do this alone."
>> When Nike Foundation's Maria Eitel and Girls Not Brides' Mabel van Oranje sat down to talk about the power of partnerships to deliver global change for girls, we caught it on film.
10:22 - Michael Anderson, CEO of the Children's Investment Fund Foundation, just announced an important new research project on the economic consequences of child marriage: "Child marriage costs lives and it costs money. The huge economic costs of child marriage are rarely discussed. Let's start a new conversation about the economic imperitive for ending child marriage."
10:12 - One of the speakers from India has this message to share on behalf of the country: "We're on a mission to eliminate extremism. I believe and I trust that Pakistan will change. It will be a long and slow journey, but I believe it will happen."
09:30 - Following on from the Girl Declaration reception we held with ICRW yesterday, senior direcctor of the gender, population and development team Suzanne Petroni is here.
>> To solidify ICRW's involvment in scaling up solutions to end child marriage and FGM, they have co-signed this commitment: "We, the undersigned, commit to working together to advance the evidence base that can better inform, support, and track programmes and policies that address FGM/C and CEFM at scale across different countries, so as to end the practices within one generation."
09:15 - UK home secretary Theresa may has just announced a £1.4m FGM prevention programme. It will set out strict new plans for ending the practices, including a national taskforce, improved police response times and anonymity in court cases: "We are making progress. And today we are taking one more step on the road towards giving women a voice, and eradicating these harmful practices."
>> This is a fantastic way to start the day, read Theresa May's entire speech from the Girl Summit for the full picture.
09:07 - UK secretary of state for international development Justine Greening talks at Girl Summit - alongside home secretary Theresa May and Yvonne Powell, principal of summit hosts Walworth Academy - with a strong message for the day: "This has got to be a global movement and today is about galvanising and inspiring everyone. Everyone has to play their part and keep going until we end FGM and child marriage for everyone, everywhere."
08:10 - Tony Lake, from Unicef, is speaking: "A girl is not a possession. Through the#GirlSummit, let's send a message to every girl in the world: you are not forgotten."
08:05 - Girl Summit has begun! Kicking off with opening remarks from UN general secretary Ban Ki-moon on screen.
08:01 - Unicef have released new data to show the need for urgent action on FGM and child marriage. It's garnered press attention from the likes of TIME Magazine and The Washington Post.
08:00 - This summit is too important to stay behind closed doors, so we're here all day, reporting live. Follow along, and tell us what you think about the commitments made as the day unfolds, with #GirlSummit.