Junior copywriter Mountford and brand strategist Sloan beat off stiff competition in the inaugural PRCA event to find the UK's best PR talent aged 28 or younger.
The pair won the award after presenting a campaign plan for a brief set by the UK charity Action For Children in front of a panel of judges on Friday.
They will now jet off Cannes Lions festival and compete against representatives from over 20 countries on Saturday 14 June. Each team will have 12 hours to build and deliver a presentation for a non-profit organisation and will be judged by a selected jury.
The winners of the PRCA’s Silver award were H+K Strategies’ Charlotte Nathan and Saamia Razvi; and the Bronze winners were Cohn&Wolfe’s Judi Bamford and Louise Fernley.