The appointment comes soon after the agency in January.
Robb will be responsible for increasing new business wins across I Spy’s core services of natural and paid search, display, social media, mobile marketing and conversion optimisation.
She joins I Spy from launching premium lifestyle site VintageSeekers.com and fashion marketing firm Dust PR, where she developed marketing, ecommerce, business and financial strategies for both companies.
Prior to that, she was group distribution director at Travelzest PLC, overseeing the digital development of the group and working closely with the team on acquisitions and start-ups.
Robb was previously managing director of Teletext Holidays from 2004 to 2006, where she was responsible for the television business both on analogue and digital platforms.
She won the Asian Women of Achievement’s Business Woman of the Year award in 2004 and was named as one of Media Week’s '30 under 30' in 2001.
Nick Jones, managing director, I Spy, said: "We are absolutely thrilled to have another heavyweight come on board.
"Nishma is joining at a time of incredible growth, both in scope and scale. I have no doubt she’ll be an immense asset in taking this growth even further."
She will join the agency, which launched in 2005, next week (7 March).
In September last year to develop software systems to improve reporting efficiency for clients.