The gift exchange happened through the website Reddit's secret Santa event, in which users swap presents across the country.
A spokesman for Gates confirmed he participated. Spokesman John Pinette says the billionaire philanthropist wanted to engage with Reddit's community and promote Heifer International, a foundation that provides seeds and animals to people in need in the developing world.
The woman, identified only as Rachel, wrote in a blog post that she was surprised to find out Gates was her Secret Santa. She received a stuffed cow toy, a signed card, a National Geographic travel book and a $500 donation to Heifer International in her name.