The appointment of JWT Worldwide to its estimated global £80m ad account follows a management reshuffle at the handset manufacturer, which resulted in the departure of vice president of global brand strategy Steven Overman and vice president of product marketing Ilari Nurmi.
In repositioning itself as a challenger brand, Nokia is hoping to reverse the long slide in its market share that saw Samsung finally break its 13 year grip on the top spot last year, with a market share of 22% to Nokia's 19.1%.
Tuula Rytilä, chief marketing officer at Nokia, said: "In many ways, we've changed the way we market Nokia and our products. At the core of Nokia brands are attributes such as quality, innovation and relevancy."
She added that Nokia is aiming to "evoke a stronger emotional response", alongside its current brand qualities such as "quality, trust-worthy, ethical and innovativeness".
"As a challenger in the mobile market, we want to be bolder in order to make our point clearer. And importantly, what we do, needs to resonate with the consumer."
Nokia is expected to focus on retail and digital marketing, to target the majority of consumers seeking out information online before purchasing their smartphones.
Third-placed mobile manufacturer Apple has also been capturing market share at Nokia's expense and recorded a 50% increase to 7.5% in 2012 from 5% in 2011.
This trend continued in Q1 2013 as the Finnish firm's share fell almost 5%, from 19.7% to 14.8%, while Apple's share rose to 9% and Samsung's increased to 23.6%.