Xerox's marketing support manager Sergio Antonio said that the firm had chosen GCI in a pitch that included several unnamed Portuguese rivals.
The one-year brief for undisclosed fees includes corporate communications, media relations and events organising for Xerox in Portugal only, Antonio said.
Xerox has not retained an external PR agency since ending its relationship with previous incumbent Joan Carrera Bom Comunicacao last summer.
Antonio said thatXerox expects GCI to liaise with other Xerox communications agencies throughout Europe.
The Lisbon-based firm will report to Xerox's European communications chief Kevin Perlmutter and to the group's marketing head Jose Clara.
Isabel Rivas will lead the account at GCI.