In an Instagram post on Thursday, Jennifer said: "Nayel Nassar, you are one of a kind. Absolutely swept me off my feet this past weekend, surprising me in the most meaningful location over one of our many shared passions.
"I can't wait to spend the rest of our lives learning, growing, laughing and loving together. Yes a million times over."
Nassar also shared the happy news on his own Instagram account and wrote, "SHE SAID YES!!...I'm feeling like the luckiest (and happiest) man in the world right about now. Jenn, you are everything I could have possibly imagined..and so much more."
The would-be couple attended Stanford University and the love blossomed there. Jennifer is the eldest daughter of Gates who has a net worth of nearly $110 billion.
According to media reports, Nassar was born in Egypt and raised in Kuwait.
He helped Egypt qualify for the 2020 Tokyo Olympics, which is their first such Olympic qualification for 60 years.
"Jennifer has also participated in professional horse riding competitions and shares a deep love for the sport," said reports.
Gates married Melinda French on a golf course on the Hawaiian island of Lanai on January 1, 1994. They have three children.
The family resides in Xanadu 2.0, an earth-sheltered mansion on the side of a hill overlooking Lake Washington in Medina, Washington.
Jennifer's mother Melinda Gates took to social media and wrote, "So thrilled for you and @mayelnassar!"
( With inputs from IANS )