Agreement had been reached with Seattle Sounders back in August for the player to join us in 2015.
Capped 10 times by the United States, DeAndre rounded off his time in Major League Soccer recently by being named US Soccer Young Male Athlete of the Year.
The 21-year-old made it into the MLS All-Star Team in his first season in 2013 - the first 'rookie' to do so in the MLS since 2005 - and earned the honour again this season.
Head Coach Mauricio Pochettino said: "DeAndre is a young player with great potential who has already achieved a lot in Major League Soccer.
"It is important for his development that he is given the time to adapt to his new surroundings both on and off the pitch and we believe that by coming to us in January it will give him the best opportunity to do so."