The former Gil Vicente coach, who has been working as a television analyst in recent years, will be responsible for scouting opposition teams and players
The 47-year-old coach, who quit the game in 2005, will serve as a scout and is charged with the responsibility of analysing rival teams and players.
"As I said a while ago, this season marks my return to work," Campos wrote on his official Twitter page before adding the hash-tag 'HalaMadrid'.
Campos is a familiar face to Mourinho, as the 47-year-old was in charge of the Gil Vicente side that ended Porto's unbeaten league run during the treble-winning campaign of the 2003-04 season.
The Portuguese, who has also worked with Leiria and Beira-Mar, has recently been working as a television pundit.