The agency won the brief after a competitive pitch through the AAR against unnamed communications planning specialists.
Rise will work alongside the Richmond marketing team to develop a communications strategy for the brands, to which Richmond is committed to investing in over the next four years.
Skinny Cow is a low-fat, premium ice-cream that is popular in the US and is currently on national UK distribution through Asda, while Fab is an established children's ice-lolly brand.
Simon Mathews, a founding partner of Rise, said: "This is a great opportunity to apply our 'find them, mind them' communications thinking, which sets out to acquire and retain more higher-value customers, bringing together direct marketing and brand-building communications opportunities in a consolidated strategy."
Kate Needham, Richmond's marketing director, said: "We saw a number of communication strategy agencies and selected Rise because we liked the way they focus communications on enhancing bottom-line performance."