The campaign, created by Indicia, will launch tomorrow (Friday), asking people to follow myIrish140 and include the hashtag #makesmeirish in their message.
Tweeters will be able to win a spot prize every 140 minutes, while the writer of the best #makesmeirish will win a 140-hour adventure tour of Ireland, which will include either taking part in a sheepdog trail or taking a hot-air balloon ride.
Sarah Rogers, Tourism Ireland’s customer engagement manager, said: "The My Irish 140 campaign is the latest initiative in our strategy to engage, inform and excite our current and prospective visitors. Social media, and in particular Twitter, can be extraordinarily powerful and, by tapping into people’s Irish connections, we’re confident that we’ll create a lot of buzz about Ireland".
Ian Bates, Indicia creative director, said: "This is an intelligent and bold campaign to capture the imagination of the audience and celebrate the diversity of people’s Irishness around the world.
"Designed to engage and excite, we believe this Twitter campaign will give potential holidaymakers a real flavour of Ireland’s rich cultural and historical landscape."
In October, Tourism Ireland called a review of its £50m global advertising and media accounts.