Cody Gakpo is the first player Liverpool has signed during the January transfer window.
Gakpo, a striker from the Netherlands, arrives from PSV, where he previously spent his whole career.
Gakpo's World Cup heroics, when he scored three goals for the Oranje, made a January transfer inevitable. A move this season had been long anticipated.
Thought to be the front-runner for the versatile player, Manchester United, PSV revealed on December 26 that they had reached an agreement with Liverpool.
Subject to receiving a work permit after Gakpo travelled to England for a medical exam, that move has already been finalised.
After his signing was officially announced, the 23-year-old said on the club's website: "I feel pretty fantastic, and I'm really pleased to be here. I can't wait to begin practising and beginning playing for this fantastic team.
"I think this is a great club for me to come in and try to show what I can [do] and try to help the team to achieve more beautiful moments than they already did in the past years.
"I think for me personally it's also good to develop here and there's a lot of great players here [who] I can learn a lot of things from."
Gakpo, who has reportedly cost Liverpool around £37million (€42m), scored nine goals and provided 12 assists in 14 Eredivisie matches this season.
The last player to contribute more goal involvement through 14 games in the Dutch top flight was ex-Liverpool superstar Luis Suarez, who had 25 for Ajax in 2009-10, the season before he joined the Reds.
Gakpo boosts a Liverpool attack missing both Luis Diaz and Diogo Jota due to injury, while he will ease the load on Darwin Nunez, who is enduring a mixed first season.