The incumbent on the offline business was the WPP-owned Maxus, while Harvest handled digital display.
PHD was awarded the business after a pitch against Carat, Starcom and Maxus.
Harvest continues to handle pay-per-click for Experian as this was not included in the review. Search engine optimisation and affiliates, which are handled in-house, were also not part of the brief.
The credit-checking service, which owns the CreditExpert brand, started a review of its media arrangements in May.
It is understood that the review was tied to an increase in advertising spend ahead of an update of Experian's consumer products. The process was led by Louise Quinn, the head of online acquisition at Experian.
Maxus had held the offline account since February 2010.
CreditExpert's most recent TV campaign, by The Red Brick Road, broke in February and positioned the brand as a financial service to help people better understand their credit profile. It used the strapline: "So you can enjoy a bright financial future."