The company, which has previously focused on direct communications through agencies including Watson Phillips Norman and the digital shop Pancentric, is looking to move towards investing in brand campaigns.
DDB will be responsible for developing the Petplan brand to both the consumer and specialist markets.
Isabella von Mesterhazy, Petplan's head of marketing, said: "We are very excited to announce the appointment of DDB.
"We are looking forward to working with them, alongside our other agencies, to help us reach the next stage of the brand's development."
Nick Fox, the chief client officer at DDB, added: "Petplan is a great company that is passionate about its work. We are thrilled to be able to help take this already successful brand to the next exciting phase of its development."