Hagger, who most recently oversaw AAR’s digital practice, will focus on all aspects of the agency’s marketing.
Her role will be primarily focused on the UK and she will report to Nigel Vaz, the senior vice-president and managing director. However, she will have some global responsibilities and will also report to Bill Kanarick, the senior vice-president and chief marketing officer.
Hagger joined AAR, which is close to appointing a replacement, in January after stepping down from Glue Isobar after more than ten years in August 2011.
She said: "The chance to work with SapientNitro to further develop their business is an amazing opportunity."
Vaz said Hagger’s "rare combination of experience, ability and insight" will help SapientNitro position its brand.