It begins in the French city of Nimes on August 19. "One is that I will participate in the next Vuelta a España starting August 19, and the second is that will be my last race as a professional cyclist".
"Hi all, I'm doing this video to inform you all of two things", said Contador.
"It's a decision I have thought over very well and I don't think there is a better farewell than in the race in my country".
Second only to five-time Tour victor Miguel Indurain in Spanish cycling lore, the 34-year-old Contador has been one of the sport's top riders for the last decade in a contentious career.
While the Spanish cyclist initially meant to retire in 2016, he joined Trek-Segafredo for one a year ago in the saddle, finishing ninth in the 2017 Tour de France.
Nicknamed El Pistolero for his attacking style and ability to mount devastating attacks in the mountains, Contador won his first Tour de France in 2007 with the Discovery Channel team before moving to Astana and winning it again in 2009.
He completed the 2017 Tour in July in ninth place overall, suffering from a couple of minor crashes and looking off the form that has seen him win seven Grand Tours.
"I'm sure it will be a great three weeks, enjoying all your affection, and I'm eager that they come".
A lengthy legal case ended in 2012 with the Spaniard ultimately being given a retrospective two-year ban. Another victory in the Tour de France and Giro from the Spaniard seized as the result of a doping scandal.
Luxembourg's Andy Schleck was awarded the Tour de France victory, while Michele Scarponi of Italy took the Giro d'Italia title.