The campaign, which spreads across TV, digital, out of home and social media, has been created by Ogilvy and Mather, with media planning and buying handled by Mediacom.
It features a series of contrasting scenes that show both negative and positive vignettes, aiming to show Coke's audience that there is "more good than bad in the world".
Coke has partnered with Kindle, Spotify and Xbox to extend the reach of its new campaign, while consumers will be encouraged to "contribute their own reasons to believe" through the brand's recently relaunched digital platform, Coke Zone.
Bríd Drohan-Stewart, marketing activation director, Coca-Cola Great Britain and Ireland , said: "For 127 years, we have been proud to create bold, thought-provoking campaigns, and the ‘Reasons To Believe’ campaign firmly follows in these footsteps.
"This campaign takes us back to the heartland of what our brand has always stood for – talking to people on an emotional level about topics that are relevant to them and spreading happiness and optimism.
"The campaign has already run successfully in 70 countries around the world and is rooted in local research. Coca-Cola as a brand has never been afraid to speak its mind and has an authentic cultural depth across the world – everyone in some way has a nostalgic connection with the brand, evoking happy memories."