The business, which was held by the Scottish agency The Union, was awarded to CDD this week following a three-way pitch against Grey London and Delaney Lund Knox Warren & Partners.
The account is a boost for the agency, which has been operating at a loss and relying heavily on its Mercedes business as its only major account.
IF launched the review back in August shortly after the arrival of Duncan Movassaghi as its marketing director. He said: "I was looking for an agency that exhibited enthusiasm and a culture that mirrored our own. I believe in CDD we've found just that."
The loss of the account will come as a blow to The Union, which had handled the business before the merger of Halifax and the Bank of Scotland in 2001,to create HBOS.
IF, which offers current and savings accounts, personal loans, mortgages and credit cards, was launched three years ago with a quirky ad to the theme of Fat Boy Slim's hit Right Here, Right Now.
It now faces tough competition from a saturated market including Egg, Smile and Cahoot.
Casper Thykier, the managing partner of CDD, said: "It felt like a really good cultural fit from the beginning. They have got ambitious targets which is how we like them."