Rooney could potentially see out the remainder of his career Stateside, and the Manchester United legend is delighted to follow in the footsteps of compatriots Steven Gerrard, Frank Lampard and Ashley Cole in making the switch.
"It is fantastic to be joining DC United at such an exciting time in the club's history with the new stadium (Audi Field) opening in just a few weeks," he told his new side's official website.
"Moving to America and MLS fulfils another career ambition for me. I have the hunger to be a success here and will give DC 100% - as I have always done for every team I have ever played for.
"When I visited earlier this summer I was really impressed with everyone I met connected with the club, and of course the new Audi Field. Now I can't wait to get on the pitch in a United shirt and join my new teammates to bring success to this club."
Rooney could make his MLS debut on July 14 if his international transfer certificate goes through on time.