Mother fought off competition from Creature London and M&C Saatchi to win the account in a process handled by Agency Insight for the brand, which is majority-owned by Coca-Cola.
101 picked up the business after a review that was also handled by Agency Insight in 2013 but did not repitch.
Mother has been tasked with developing Innocent’s communications across its pan-European business as the 17-year-old brand continues its expansion drive beyond the UK.
Tim Clarke, group marketing and innovation director at Innocent, said: "We were very impressed by all of the agencies we met throughout the pitch process.
"Mother in particular really grasped our ambition, and we're excited to have them on board as our agency partner as we drive the continued growth of the business across Europe and reach our goal of becoming Europe's favourite little juice company."