The Red Brick Road pitched against Beattie McGuinness Bungay, Cheethambell JWT and Mother London for the work, which will lead to a £4 million campaign.
Soreen’s managing director, Paul Tripp and its marketing manager, Hannah Flannery, managed the process in house.
The Red Brick Road will work with Flannery to reposition Soreen as a "versatile snack brand".
The campaign featuring TV, print, digital and social media will run in mid-2014. It could support the new flavours of Soreen loaves launched recently to celebrate its 75th anniversary, such as the Soreen Limited Edition Chocolate Malt loaf.
Tripp said: "Not many agencies are as commercially-sharp as they are creatively-strong. TRBR really impressed us by leaving no stone unturned in their pitch, and we’re very excited about our New Year anniversary celebrations.
David Miller, the managing director of TRBR, said: "Soreen is a fantastic British brand – it is great to be developing this ATL advertising campaign to support Soreen’s iconic powerbrand status. We’re itching to get started."