The Portuguese manager is fresh from winning the Europa Conference League title with Roma.
Mourinho was an assistant coach to Louis van Gaal for three seasons before leaving Barca in 2000 to take on the role of Benfica manager.
"I never had him as a first team coach but as an assistant," Barca coach Xavi once recalled of Mourinho's time at the club.
"He was aggressive and taught us football concepts."
Mourinho won a LaLiga title, a Copa del Rey and a Spanish Supercup in his three seasons at Madrid.
His return to the Camp Nou will add spice to the Gamper Trophy, an annual friendly match held in August that acts as a curtain-raiser to Barca's campaign.
Roma already faced Barca at the Gamper in the 2015 edition, with the Catalan giants winning 3-0.
Barca beat Italian giants Juventus in the previous edition.