Son, who is in talks over a new deal with Spurs, has signed with CAA Base, a division of CAA Sports, which will represent him both on and off the pitch.
Mourinho, Cristiano Ronaldo, Dele Alli, James Rodriguez and Bernardo Silva are among the firm’s other clients.
Son’s form this season, where he has scored 10 goals in nine games, has seen him catapulted into the limelight and his switch to CAA Base will help increase his profile off the pitch significantly.
Mourinho is keen for the club to sort a new long-term deal for the 28-year-old, recently saying: “I wish. He deserves one. The club knows that and sooner or later, without any pressure, they will arrive into a decision.”
Spurs are next in Premier League action this Sunday as they welcome Graham Potter's Brighton to the Tottenham Hotspur Stadium.
Son will hope to continue his prolific partnership with Harry Kane. Son's header from Kane's flick-on during the 1-0 win at Burnley last Sunday was the ninth time this season the duo have combined for a Premier League goal - and 29th in total.
Brighton arrive in North London off the back of a 1-1 draw with newly- promoted West Brom. Brighton have five points from their opening six league fixtures.