The brief is thought to be worth in the region of £1m per year.
PRWeek understands that Weber Shandwick, which previously held Aldi's corporate and public affairs briefs too, was in the final pitching process for the consumer account alongside Red and Good Relations.
Aldi UK comms director Mary Dunn said: "Having undergone a tender review of our retained UK consumer PR and social media agencies we are delighted to confirm the appointment of Red Consultancy."
Red will handle PR for some of Aldi's consumer grocery categories, as well as its social media account, a spokesperson for the supermarket group told PRWeek.
Mike Morgan, CEO at Red Consultancy, said: "We are excited to be chosen to help tell the next chapter of Aldi UK's amazing story."
Red will join Aldi's existing roster of UK agencies, which includes Clarion Communications, Burson-Marsteller and Citypress.
Citypress won Aldi's UK corporate PR account in June 2015, replacing Weber Shandwick, which had held the brief since 2008.
Weber had also previously handled Aldi's UK public affairs brief, until this account was won by Burson-Marsteller in 2014.
Weber Shandwick UK and EMEA CEO Colin Byrne said: "Working in partnership with Aldi for the last eight years, we are delighted to have played a role in helping them to become the major force in the UK grocery retail trade that they are today."
A spokesperson for the agency said Weber Shandwick Scotland would continue to deliver regional PR and social media activity for the supermarket.
Clarion, meanwhile, has worked with Aldi for the past four years on consumer campaigns.
Aldi operates in 20 countries globally and in September last year it said it would invest £300m in its UK and Ireland stores, as the group planned to extend its current 785 outlets to 1,000 by 2022.