Byers, 32, best known as Andre Lyon in the drama series, asked Gealey for marriage on her 31st birthday on Sunday, reported Us Weekly.
"He surprised her on her birthday... He popped the question and she was totally surprised and elated. She can't stop looking at the ring! They celebrated all night," a source said.
Gealey, 31, who plays Anika Calhoun on the show, celebrated her engagement and birthday with fellow co-stars.
Byers also took to Instagram and shared a photo collage of her birthday bash.
"Had so much fun celebrating @gracegealey's life! Happy Birthday to an exquisite human being! Thank you @kinmontchicago for hosting us. Amazing spot, wonderful food, UNFORGETTABLE night," Byers captioned the picture.