British media reported that Liverpool paid Aberdeen £4.5 million ($5.50M) plus add-ons for the 18-year-old.
Ramsay recorded nine assists in 33 appearances across all competitions for Aberdeen in the 2021-22 season as they narrowly avoided relegation from the Scottish top-flight and reached the final round of qualifying for the UEFA Europa Conference League.
"It was a dream come true to play for Aberdeen, and now to be at one of the biggest, if not the biggest club in the world, it's a massive achievement and I'm looking forward to trying to show the fans what I've got," Ramsay said.
"There's obviously a pathway here," he said. "That's one of the reasons I chose it as well. It's not just a massive club, they give young players chances in the first team.
"So if I can come in in preseason, put my mark down, then there's no reason why I can't push to get in the first-team squad."