The start-up will launch with a pan-European Unilever ice-cream brief that poses a threat to McCann Erickson, Unilever's principle incumbent on its ice-cream brands.
Clarke has persuaded Shearer, the former Leo Burnett and Wieden & Kennedy executive creative director, to be a partner in the new agency, as well as its chairman and creative director.
The agency will position itself as a creative and strategic hotshop that operates with as few middlemen as possible. Shearer will set up with a staff of eight, including a senior planner, two junior account executives, an office manager and production staff. He has already secured offices in Clerkenwell, central London, which will open its doors for business next week.
Nitro will only target large international clients which need quick turnaround creative work for their brands. Creatives and planners from the agency will base themselves within clients' offices to improve their understanding of the advertiser's problems and to speed up the turnaround of work.
Shearer told Campaign: "If agencies of 300 people are not able to meet clients' needs they are going to have to change."
The agency has already developed ideas for a pan-European branding campaign for Unilever's ice-cream range. The agency beat McCann Erickson's Milan arm in a two-way pitch for the business. Clarke's existing strong ties with Masterfoods are expected to see the start-up land Mars briefs in Europe.
However, a spokesman for Masterfoods said: "We are not planning to do anything different. All brands are planning to stay where they are."
Nitro's European launch follows the capture of the US Twix account in August. Sources close to Masterfoods have speculated that Mars is looking to shift more of its business to creatively led shops around the world.
This would pose problems for Grey, which currently holds 22 Masterfoods brands including the Mars Bar and Galaxy ranges and Milky Way.
Clarke founded Nitro in China in 2001. He has since set up offices in Sydney and New York and has numerous satellite offices across Asia.
Nitro is the second advertising network to be established by Clarke.
He previously set up Pure Creative, which operated in Australasia and Asia and counted Mars, Procter & Gamble and Coca-Cola among its clients. The network was sold to D'Arcy in two chunks in 1999 and 2000.