GH will also pick up project work in Europe for the account, worth more than £200,000 annually.
Nelson Bostock and five other agencies originally pitched for the brief in January. September will see a transition period before GH begins work on a major marcoms drive.
GH co-managing director Jonathan Hughes heads the account, reporting to NEC UK MD David Payette and European department corporate comms manager Chris Shimizu.
NEC's product range includes mobile phones, semi-conductors and broadband network systems.