The 19-year old Honduran winger leaves the Washington outfit after becoming a key senior player with DC following his Homegrown signing in 2010. Reports suggest that the deal is worth around $3million.
"It has been very rewarding to watch Andy grow and develop into becoming the special player that he is," DC United general manager Dave Kasper said in a club statement.
"This transfer is a testament to the hard work of our Academy staff, to Ben and his staff for their patience and vision, and to the MLS Homegrown Player initiative.
"We wish Andy all of the success in the world and we look forward to watching his career blossom. Looking ahead, we plan to focus on utilizing our resources and flexibility to continue to build our team."
Najar wrote an open letter to DC fans thanking both them and the club for assisting in his development. Below is an excerpt.
I leave D.C. United after many special years. I would like to thank everyone connected to the club for everything that has been done to help me and my family since I joined the academy years ago.
A special thanks to my coach Ben Olsen and all of his staff. I came to D.C. United and chose #14 because I wanted to follow in his footsteps. He has been a great coach and more importantly an excellent role model for me to learn from.
I wish the club the best in the years to come and hope to be able to play in front of you all one day in the future.
May god bless you all, Andy Najar