She appealed to "any woman or girl or man - I believe men also must be feminist, without question" to continue the fight for equal rights for which the suffragettes blazed a trail more than a century ago.
The singer said: "They were sacrificing themselves for us ... to have access to the democratic vote, to education, to job opportunities - the fight continues."
"The problem is in our country we have amnesia. We forget that people sacrifice so much to give us the things we take for granted."
Speaking on Mother's Day, she said: "As a mother, I've realised I've got such a privileged life and I've seen the disparity, so I feel indebted and I feel that I must stand in solidarity.
"To be a mother is a very wonderful thing - please remember that around the globe there are women delivering babies today - those girls that have no access to healthcare, to reproductive health protection ... have a moment to reflect on that."
Lennox was speaking at a rally organised by Care International to launch the start of the Walk In Her Shoes campaign, which is asking people to raise money for the charity by walking 10,000 steps a day for one week in March, The Press Association reported.
She was joined by a host of public figures including London mayoral hopeful Sadiq Khan, rights campaigner Bianca Jagger and International Development Secretary Justine Greening.
Lennox added that today was not just a "commemoration" but an "encouragement to keep this fire burning, this flame to illuminate the disparity - to understand that there's so much disempowerment globally".
"And it's very hard to get that message through, because we're busy, we have our busy lives and our very comfortable existences.
"So we don't think about the world as it stands for millions of women who are uneducated and have no access to resources."
Hundreds of people packed the Scoop amphitheatre on London's South Bank to listen to speeches from survivors of female genital mutilation (FGM), politicians and feminist campaigners, before setting off on a march.
A crowd of suffragettes, in period dress and wearing sashes emblazoned with the slogan "Deeds not words", sang and chanted feminist anthems.
Dr Helen Pankhurst, great-granddaughter of suffragette Emmeline, was leading the procession with her daughter and said she could not think of a better way to mark Mother's Day.
She added that she felt "really honoured" and "proud" to have such a revolutionary ancestor but warned there was still a need for solidarity and activism.
She said: "It's about celebration, it's about being together, it's about sisterhood.
"We can do that in many ways, we can do that through social media but there is still a value in being out in the streets, walking together shoulder to shoulder as the suffragettes did 100 years ago."
She added that this year "we'll also be thinking about the many refugees who have trekked hundreds of miles to find safety, many of them mothers, forced to carry their children from one danger zone to the next".
Bianca Jagger said the turnout was "inspiring" and echoed Dr Pankhurst's sentiment that it was important for feminists to physically come together.
Lamenting the lack of women in Parliament, and in leadership positions across the globe she said: "Every year when I march ... I feel really saddened by the fact that we are not thousands, that we are not tens of thousands - millions of women walking throughout the world to say the time has come for us to really have gender equality.
"I am on social media, I believe in social media ... and it's wonderful that we are there. But it's important that we come together ... we need to embark upon a non-violence revolution to achieve gender equality and to defend women's rights."
Although he did not attend the march, Labour leader Jeremy Corbyn announced that he was supporting a campaign to erect a statue of Mary Wollstonecraft in celebration of "the women who have shaped our country", saying "It's time to redress the bias of statues and memorials towards men."