Pacquiao tipped the scales at 66.1 kg (146 pounds) and Horn came in at 66.3 kg (146 pounds) at the official weigh-in.
Unbeaten Horn, a former schoolteacher, said he was ready for the biggest moment of his boxing life.
"Game face is on. School's out," Horn told reporters.
"I'm nice and relaxed. I'll probably still maintain my relaxed state until fight day but I'm really looking forward to getting out there tomorrow and getting the job done."
Pacquiao, 38, an eight-weight world champion and one of the greatest fighters of his generation, did not make any comments and quickly left the weigh-in ceremony.
"It's never easy to lose that much weight," Horn said.
"I'm going to feel a lot better very soon. I've got to go eat as soon as I finish with the media, keep drinking, keep up with the fluids all day, all night."
Trainer Glenn Rushton said Horn looked superb in his final training session late Friday.
"He was brilliant, he was just like I want him to be. He was toey, he was just electric," Rushton said.
"I know when he's hitting the pads there's just extra pop there in his punches. I just felt the hunger. That's what I look for."
The Pacquiao camp throughout this week has said it is anticipating a "short and sweet" win over Horn, a 2012 Australian Olympian, before an expected 50,000 crowd at Suncorp Stadium on Sunday.
The Pacquiao team has spoken of setting up another showdown with the unbeaten Floyd Mayweather, who outpointed 'Pac-Man' in the "Fight of the Century" two years ago.
"We're chasing a rematch with Floyd Mayweather and we know he has to score a spectacular knockout win over Jeff Horn if that's going to happen," Pacquiao's trainer Freddie Roach said.
"I'm looking for a big win in Brisbane so we can go on to bigger and better things.
"I've been looking for a big knockout from him for a long time now and I think you're going to see it in this fight."
Pacquiao has beaten some of the best -- Oscar de la Hoya, Shane Mosley, Ricky Hatton, Jesse Vargas -- while 29-year-old Horn is stepping up in class substantially in the WBO title fight.
Pacquiao, who is also a senator in the Philippines, regained the welterweight world title belt he lost to Mayweather when he knocked Jesse Vargas down in the second round and cruised to a unanimous decision in November.
He will be making his first defence against Horn after a big-money fight with British boxer Amir Khan in the United Arab Emirates fell through earlier this year.