The agency triumphed after a pitch against Clemmow Hornby Inge and HHCL & Partners.
The swimwear brand, owned by the Pentland Group, has also made a media decision, recently appointing CIA to the business. The appointment brings more Pentland business into the CIA portfolio, which includes the Ellesse and Kickers brands.
Speedo has not advertised heavily in recent times, with previous creative work handled by Pentland in-house. However, Speedo has appointed Fallon for a long-term brand push with a brief to build on its heritage.
It is not yet known across which media forthcoming work will run. However, it is expected to run in Speedo's key markets of the UK, Germany, France and Italy.
Robert Senior, a partner at Fallon, said: "We're delighted to be working with Speedo. It's the sort of brand and challenge we thrive on."
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the Forum here.