Baldwin, who has been involved with Hempel for more than a year, "slipped the ring into a glass of cranberry juice ... [and] upon finding the ring amongst the ice, Robin exclaimed, 'Yes!'" he told People magazine.
Baldwin, 54, said he designed the 5-carat ring himself.
"I couldn't be more overjoyed Robin said yes," Baldwin added. "Next to the birth of my children, this is the happiest day of my life."
Baldwin has four daughters and a son from previous relationships.