DeAndre has signed a four-year contract and will remain with Sounders before joining us ahead of the 2015/16 season.
Capped seven times by the US, DeAndre caught the eye with his performances at this summer's World Cup. Born in Seattle, he joined Sounders' Academy in 2010-11 and became their first home-grown player when he signed in January, 2013.
The 21-year-old made it into the MLS All-Star Team in his first season last year - the first 'rookie' to do so in the MLS since 2005 - and earned the honour again this season for the recent MLS All-Star game against Bayern Munich.
DeAndre has now played 52 times for the Sounders in all competitions and lined-up against us in our 3-3 friendly draw at CenturyLink Field on July 19, the first match of this summer's Tour of North America.