The watch is to be promoted to men in Europe, India and Mexico as a gift for women on Valentine's Day.
The Yahoo! Europe sales team negotiated the deal from its London headquarters.
The week prior to Valentine's Day, the "Shake the Heart" watch will feature in roadblock advertisements on the front pages of Yahoo! Sports in Germany, France, Spain and Italy.
The activity, which starts on 8 February, will culminate in an interactive home page event in these countries on Valentine's Day, with the exception of Italy, which will host the event on 13 February. Users will be able to interact with the "Shake the Heart" creative and send messages to loved ones directly from the Yahoo! home page, as well as view the "Shake the Heart" watch.
This is the first time Swatch and Yahoo! have worked together and the first time the search engine has provided an email offering on their homepage in an international advertising campaign.