As of January 15, the Swiss watchmaker - already heavily involved in equestrian sports - will become the main sponsor of the International Equestrian Federation.
In Lausanne, Her Royal Highness Princess Haya, president of the FEI, and Nayla Hayek, chairman of the Swatch group which ownsLongines, will make the partnership official.
Longines will also become official timekeeper of the series and provide the official watch.
"It is the beginning of a new era for our sport and the FEI," Princess Haya said. "Longines always had a strong presence in our community and our new partnership is a real celebration of a common passion.
"This long term partnership with Longines will revolutionise the way we can promote our sport throughout all our disciplines."
Longines will also replace Jaeger LeCoultre as title sponsor for the Global Champions Tour.
The brand is already involved with Indoor Grand Slam, the next leg of which is the Longines Hong Kong Masters in early March.