Total Media replaces MediaCom, which has held the account with the frozen seafood since 2000.
Young’s said Total Media, which bills itself as a "behavioural planning agency", would support its three-year growth strategy.
The agency joins Young’s existing partners, which include creative agency Quiet Storm, digital agency Activation and brand design agency Springetts.
Yvonne Adam, marketing director of Young’s Seafood, said: "It’s an extremely challenging time for brands to connect with consumers and in order to maintain our position as the UK’s leading fish and seafood business we needed to make a significant step change with our media buying.
"Total Media’s deep knowledge of multiple channels and its approach to audience insight proved to us that they were the right team to work with."
Tom Laranjo, managing director of Total Media, added: "Gaining new customers in a crowded market is a challenge, regardless of brand prominence. Using the latest behavioural science and technology, Total Media will help Young’s maintain its position as market leader."
Young's sales in the 12 months to March 2018 were up 4.9% to £188.7m, according to data from IRI.