Shine will start work on the account immediately. It was previously held by Mischief.
The appointment comes after Zizzi's and ASK Italian, owned by European private equity firm Cinven, were sold last year to Bridgepoint for a sum of £250m.
Jo Fawcett, marketing director at Zizzi, said: "We were really impressed with Shine’s creativity and experience of running integrated campaigns talking to different audiences."
Shine’s MD Lawrence Collis said: "We are looking forward to delivering an exciting social and traditional PR campaign that creates deeper engagement for existing Zizzi customers and using our analytical tools to enable us to identify new audience opportunities for it."