The 33-year-old model is engaged to marry Snapchat co-founder and CEO Evan Spiegel.
She made the announcement on her Instagram account - using a Snapchat filter - on Wednesday, with a photo of a diamond ring and the caption "I said yes!!!"
This will be the second marriage for Kerr, who was previously married to actor Orlando Bloom. They have a 5-year-old son together.
Spiegel, 26, has never been married.
He co-created Snapchat when he was a student at Stanford University.