"We've told our moms so now we can tell you. Yesterday we exchanged engagement bracelets," Walsh said via Twitter Monday, alongside a photo of his and Siriano's hands wearing the bracelets.
Siriano also posted the photo on his online account, Zap2it.com said.
The couple have not yet announced a wedding date.
Siriano won Season 4 of "Project Runway" in 2008 and went on to have a successful career as a fashion designer.
Zap2it.com said Walsh is a visual and recording artist who has created the music for many of Siriano's fashion shows.