MacKenzie Bezos, who has written two novels and is an American Book Award winner, didn't specify how she would distribute the US$18b earmarked through the Giving Pledge.
Her philanthropy to date has focused on marriage equality, transitional housing for homeless families, and college scholarships for undocumented immigrants brought to the US as minors. In 2013, she founded Bystander Revolution, an anti-bullying organisation, for which she is the executive director.
She also worked at Amazon - where she was an accountant and negotiated contracts - in the early days, long before it grew into the US$905b retail behemoth it is today. Unlike her former husband, MacKenzie Bezos has kept a relatively quiet profile and hasn't had a public role in Amazon in years.
The couple announced their split in January after 25 years of marriage and four children. Soon after, Jeff Bezos' relationship with a former news anchor was made public, sparking headlines and a public battle between the mogul and the National Enquirer and its parent company, American Media Inc.
The couple finalised their divorce in April. Under the terms of their settlement, he retained 75 per cent of the couple's Amazon stock and voting power over their combined shares. She was awarded roughly 4 per cent of the company.
Jeff Bezos, the world's richest man with an estimated fortune of US$100b, also was awarded all of the couple's joint holdings in the Washington Post and the space flight company, Blue Origin.
Jeff Bezos has not joined the Giving Pledge. But last year, he dedicated US$2b to help homeless families and launch a network of preschools. The commitment made him the country's largest donor in 2018.
In September of that year, he and MacKenzie Bezos had given US$10m to the veterans-focused super PAC With Honour, marking their first major political venture.
Still, the Amazon CEO has been criticised for not doing more, especially when compared with Gates, Buffett or Zuckerberg, who has said that he and his wife, Priscilla Chan, expect to donate 99 per cent of their Facebook shares to such causes as eliminating "all disease in our children's lifetime."
After the Giving Pledge announcement, Jeff Bezos tweeted that his ex-wife is "going to be amazing and thoughtful and effective at philanthropy, and I'm proud of her."
The Giving Pledge was launched in 2010 by Buffett and the Gateses after having "conversations with philanthropists around the world about how they could collectively set a new standard of generosity among the ultrawealthy," according to the Pledge's website.
Donors have given to a range of causes, including refugee aid, disaster relief, education, women's empowerment, medical research and environmental sustainability. The Pledge's public face is intended to draw more people into philanthropy and get signatories to be more charitable earlier in life.
This year's 19 Pledge donors include WhatsApp co-founder Brian Acton and Brian Armstrong, CEO and co-founder of the cryptocurrency company Coinbase. The list now includes 204 donors from 23 countries committed to giving away half of their wealth to charity during their lifetimes or in their wills.
