Liverpool had to fight off interest from other clubs for Mac Allister and always intended to get some of their transfers done before pre-season, to give them more time to settle in.
They believe the 24-year-old, who scored 10 Premier League goals as he helped Brighton to their highest-ever finish of sixth in the top flight, can occupy any of the three midfield positions in Klopp’s side.
The midfielder told Liverpoolfc.com: “It feels amazing. It’s a dream come true, it’s amazing to be here and I can’t wait to get started.
“I wanted to be in [from] the first day of pre-season, so it’s good that everything is done. I’m looking forward to meeting my teammates.
“It was a fantastic year for me – World Cup, what we achieved with Brighton – but now it’s time to think about Liverpool and try to be a better player and a better human being every day.
“Since I won the World Cup, I said that I want to win more trophies and I think that this club will help me to do that – that’s the aim and when you are in a big club like this one you have to win trophies. So, that’s what I want.
“Since I arrived here, I can see how big this club is – the players we have, the staff, everyone. I’m really pleased and looking forward to playing for this club.”
Liverpool had identified Mac Allister as a key target even before the World Cup, where he set up Angel Di Maria’s goal in the final against France, after first tracking him when he was still playing in South America.
The deal was the last completed by outgoing director of football Julian Ward, with his successor Jorg Schmadtke now taking the lead in Liverpool’s transfer business, and was aided by the club’s long relationship with his agent Juan Gemelli, who was involved in Philippe Coutinho’s move to Anfield in 2013.
Liverpool believe that Mac Allister, like Mohamed Salah, Roberto Firmino and Virgil van Dijk, had to fight his way to the top, rather than being fast-tracked, and have a history of successful signings of players aged between 23 and 25.