That honour goes to Google Android's Friends Furever campaign, featuring some surprising animal friendships. The ad has attracted more than 6.4m shares across Facebook, Twitter and the blogosphere worldwide since its launch in February.
The ad, which has been viewed nearly 20.6m times, was head and shoulders ahead of the competition, with Disney’s Surprise Shoppers advert taking the second spot in Unruly’s annual Top 20 Global Video Ads Chart with 3.9m shares.
In fact Android's ad has been crowned the most shared ad of all time - ahead of last year’s top ad, Activia’s World Cup ad “La, La, La”, which has attracted 6.1m shares across social media since its launch in 2014.
In third place was a Buzzfeed Video for Purina pet food about one man and his pup (3m shares), while ads for Budweiser and Kleenex continued the animal friendship theme.
See below for the full top 10.
Not much in the way of recognisable British brands among them. But considering they were released just a few days ago, John Lewis and Sainsbury's have done well to get onto the top 20 - and could nudge further up the list before the end of the year.
Man on the Moon, run in conjunction with Age UK, made it to 17th place with 700,000 shares, while Mog’s Christmas Calamity, which supports charity Save The Children, was 19th with 630,000 shares.
Unruly’s managing director of EMEA Oliver Smith said: “We’ve been collecting and analysing consumer data on video consumption and sharing patterns since 2006 and one of the key drivers to video shareability is emotional intensity - how an ad makes a person feel.
“From the joy you feel when your pup welcomes you home to nostalgic memories of your childhood pet, animals can tap into a wide range of emotions that have broad appeal. By placing the focus on friendship and shared experiences, advertisers in 2015 have successfully used dogs, cats and other furry friends to provoke strong feelings of warmth and well-being.”