The agency secured the business without a pitch, and will now be responsible for launching the brand's first TV ad, due to break next month, as well as a redesign of the company's website.
At the same time, CHI's sister agency MCHI has been appointed by Interparcel to handle the brand's media planning and buying.
Interparcel was launched in 2004 to allow businesses and individual consumers to order and arrange parcel deliveries online.
The company couriers around one million packages a year, using the support of major delivery networks such as DHL to help it distribute packages.
Interparcel has not previously spent significant amounts on advertising.
However, it is looking to build its brand to ensure faster growth of its business.