Ms. Scott has devoted much of her time recently to philanthropic efforts benefiting women-led charities, food banks and Black colleges, among other institutions. Since her divorce, Ms. Scott has given away more than $4 billion of her fortune, according to a post she wrote on Medium in December.

In a post dated Saturday on Ms. Scott’s page on the Giving Pledge website, for billionaires who have promised to donate most of their fortune to philanthropic efforts, Mr. Jewett signed on to her commitment.

“It is strange to be writing a letter indicating I plan to give away the majority of my wealth during my lifetime, as I have never sought to gather the kind of wealth required to feel like saying such a thing would have particular meaning,” Mr. Jewett’s post says.

“Dan is such a great guy, and I am happy and excited for the both of them,” said Mr. Bezos in a statement provided by an Amazon spokesman.

Ms. Scott and Mr. Jewett couldn’t immediately be reached for comment on Sunday.

Ms. Scott and Mr. Bezos, both Princeton University graduates, met while working at a hedge fund in New York. She helped him start Amazon in 1994, and is the author of two novels. Her Amazon author page now says that she “lives in Seattle with her four children and her husband, Dan.”

At the time of their 2019 divorce, after 25 years of marriage, Mr. Bezos was the wealthiest person in the world, with his stake of more than 16% of Amazon. Ms. Scott received 4% of Amazon’s shares as part of their divorce settlement, though Mr. Bezos kept voting rights for those shares.

Ms. Scott joined the Giving Pledge in May 2019, shortly after terms of her divorce with Mr. Bezos were finalized. The pledge was started by Bill and

Melinda Gates

and

Warren Buffett

in 2010. Mr. Bezos hasn’t joined the pledge.

Amazon’s business has been a major beneficiary of the pandemic, driving up its stock price. Mr. Bezos, after jostling for a time with

Elon Musk

for the title, again ranks as the world’s richest person, with a net worth of around $177 billion, according to wealth rankings by Forbes and Bloomberg. Ms. Scott ranks the 22nd richest person, at around $53 billion.

Mr. Jewett is a teacher at Lakeside School, according to the school’s website.

“In a stroke of happy coincidence, I am married to one of the most generous and kind people I know—and joining her in a commitment to pass on an enormous financial wealth to serve others,” Mr. Jewett said in his Giving Pledge letter.

Write to Dana Mattioli at dana.mattioli@wsj.com