The 27-year-old designer, who trained with Vivienne Westwood and has designed for stars including Cheryl Cole and Jessie J, has also been appointed as creative director of the Scottish jewellery firm.
Mr Ross, who is shortlisted for Scottish Young Designer of the Year at the 2012 Scottish Fashion Awards, has designed a new dress for Rox's sales consultants which includes a structured neckline and a feminine silhouette. He will also be responsible for all creative parts of the business.
Mr Ross, part of Design Collective Scotland along with shoe designer Emily Lamb, said: "The decision to join Rox ultimately grew from having the pleasure of hosting an event with Design Collective Scotland where we showcased our spring/summer 2012 collections in the Thrill Room of the Argyll Arcade store earlier this year.
"After collaborating with Rox and seeing how fashion-focused the brand is and how committed it is to supporting Scottish talent, I was very impressed with the brand ethos, and a joke about working with the brand all of a sudden seemed like a good idea."
Kyron Keogh, managing director of Rox, said: "We are thrilled that Marc has joined the team at Rox and we already have some really exciting plans in place.
"As a company we've always had a strong fashion-led approach, and when we met Marc we were impressed by his artistic vision and attention to detail. Working together seemed like the natural progression.
"Marc's talents transfer incredibly well into the jewellery industry and we believe that he has the potential to create collections as beautiful and diverse as talented jewellery artisans like Shaun Leane and Theo Fennell."
Mr Ross will compete against Obscure Couture, Isolated Heroes, Graeme Armour, Hayley Scanlan, Jennifer Morris and Rebecca Torres to be named Scottish Young Designer of the Year at the Scottish Fashion Awards in June.