Pacquiao, an eight-weight world champion, will put his WBO welterweight title on the line against the undefeated Horn.
"We signed the Jeff Horn contract this morning. Fight is July 2 in Brisbane, Australia," Pacquiao's adviser Michael Koncz told French news agency AFP.
The bout will be outdoors at Suncorp Stadium on a Sunday afternoon, timed to coincide with a prime-time Saturday night telecast in the United States.