The agency won the business in a final shoot-out against Saatchi & Saatchi.
Nationwide’s long-standing previous incumbent Leagas Delaney was also involved in the pitch and VCCP and Mother were on a longlist, but went out of the running at an early stage.
The review of Nationwide's £20m ad business started at the end of last year and was handled through intermediary Agency Insight.
Nationwide launched a major TV campaign, created by Leagas Delaney, last year featuring the cast of characters from the TV comedy series Little Britain.
The agency has worked on the Nationwide account on and off since 1985.
18 Feet & Rising was launched in December 2009 by the former Fallon directors Jonathan Trimble, Matt Keon and Tim Millar and works for clients including Freeview and Selfridges.