The deal will run from November until February next year. Tetley will sponsor Andy Peebles' weeknight evening show using its iconic Gaffer character to promote Tetley decaf to the Smooth Radio audience.
The deal was brokered by GMG Radio Solutions and MediaVest.
The agreement also involves a week-long promotion in Mark Goodier's morning show in January, offering listeners the chance to win £1000 every day.
Special promotional packs of Tetley decaf featuring Smooth Radio's logo and a snapshot of the Smooth Radio playlist, ways to tune in and the station's presenters will begin to appear on supermarket shelves next week.
The special packs also offer tea drinkers the chance to win a Pure DAB digital radio.
Michelle Colley, Tetley Decaf brand manager, said: "This is an exciting promotion for us. Tetley decaf is the best-selling decaf tea in the market and this promotion will take us directly to thousands of potential new Tetley decaf fans.
"It also gives us a chance to say thank you to those who are already loyal to Tetley."
Jonathan Gillespie, commercial director at GMG Radio, said: "This is a great way of showcasing how radio stations and media agencies are using creative thinking when it comes to commercial partnerships.
"Both Tetley and Smooth Radio will achieve huge brand exposure to their target audiences. We're a nation of tea drinkers and what could be a more relaxing experience than a cuppa whilst listening to the soulful sound of Smooth."
According to yesterday's Rajar results, in the final quarter of Smooth Radio's first year as a national service, the station reported an average weekly audience of 3.32 million between 27 June 2011 and 18 September 2011, up 9% year on year and 3.7% on the previous quarter.
Follow Mark Banham on Twitter @Banham72