E! News said Murgatroyd accepted Chmerkovskiy's proposal Saturday night in Miami. They have been dating off and on since 2012.
"I'm in love with you, and I want to be in love with you for the rest of my life," Chmerkovskiy declared during the third night of performances for SWAY: A Dance Trilogy.
"She said 'yes,'" he later posted on Instagram, along with a photo of the happy moment.
Murgatroyd and Chmerkovskiy have both competed on TV's Dancing with the Stars.