Grange was hired to help spearhead the agency’s new division and strengthen its social media offering, but left in recent weeks.
He joined from Apple, where he had been head of pan-European iPad PR for 18 months.
It is understood the agency is not currently seeking a replacement for Grange, who will now act as a consultant.
W founder Warren Johnson confirmed the departure, adding: "Nick has done an incredible job of setting up our technology division, which now boasts clients such as Huawei, Jambox and Siemens."
Before his time at Apple, Grange was European PR director at Activision, where he led campaigns for games including Call of Duty.
His two decades in consumer technology also included establishing the Xbox in the UK as Microsoft’s head of UK PR.
It is not known whether Grange, who could not be reached for comment, is to take up another role.