"I wanted you all to hear it from me 1st before u saw it on the news... I will be signing with the Washington Redskins and I'm very excited about the opportunity in front of me.
"I want to thank all Colts fans from the bottom of my heart for all the love and support you've shown me the past 4 years and I hope that at some level u will still follow my career, as I will continue to share my life with you on here..."
The Colts had bid to keep Garcon and are also expected to lose Reggie Wayne, who is now a free agent.
Bill Polian drafted Garcon out of Mount Union in the sixth round in 2008. Now an ESPN analyst, Polian said Garcon is a great match for Washington.
"He needs refinement with his route running,” Polian said. “... He is a perfect fit with the West Coast offense.”
The Colts lose valuable size and speed, though Garcon has work to do to prove himself a consistent weapon.