Simpson, 29, made the jubilant announcement on Monday via Twitter, posting a photo of the two — and her huge sparkler! -- with the caption: "My baby love and I are ENGAGED!!! Hallelujah Hawaii !!!!!"
Ross, 25, posted the same photo on his account captioning it: "The love of my life said YES!!!!!!"
Simpson's new fiancé is the son of famed singer Diana Ross and the two went public with their romance last July.
Simpson and Wentz have one 5-year-old son, Bronx, together.
Congratulations to the happy couple!