The 34-year-old singer and 31-year-old NFL star announced the news Thursday on Instagram.
Ciara and Wilson already have a 2-year-old daughter, Sienna Princess. Ciara is also parent to 5-year-old son Future Zahir with her ex-fiancé, rapper Future.
Ciara showed her baby bump in a photo Wilson took in Turks and Caicos. The picture shows Ciara posing in profile on a ledge.
"Number 3," she captioned the post.
Wilson posted a selfie on his own account that shows Ciara posing in the background.
Singer Anna Sedokova and Coach creative director Stuart Vevers were among those to congratulate Ciara and Wilson in the comments.
"Congratulations," Vevers wrote alongside a star-eyes emoji.
Ciara shared a slideshow of photos Wednesday with Wilson, a quarterback for the Seattle Seahawks, and her kids at the Pro Bowl.
"Pro Bowl 2020. Family Adventures. Family Fun," she wrote.
Ciara released her seventh studio album, Beauty Marks, in May. The album includes the singles "Level Up," "Dose," "Greatest Love" and "Thinkin Bout You."