Liverpool sign midfielder Alexis Mac Allister from Brighton for a reported £35 million
Financial details of the transfer were not disclosed but British media reported that the fee for the Argentine midfielder was 35 million pounds potentially rising to 55.
"It feels amazing. It's a dream come true, it's amazing to be here and I can't wait to get started," Mac Allister said in a statement.
"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."
Mac Allister helped Brighton secure European football for the first time in an outstanding 2022-23 campaign, scoring 10 league goals in 35 appearances as they finished sixth in the Premier League.
The Argentine, who signed a new contract with Brighton in October, joined the south coast club in January 2019 and was loaned back to former team Argentinos Juniors before making his Brighton debut in March 2020.
He has since scored 20 goals in more than 100 appearances for the club in all competitions.
The midfielder has 16 caps for Argentina and played six games of their 2022 World Cup-winning campaign, including the final, where Lionel Scaloni's side beat France on penalties.
Mac Allister is Liverpool's first signing of what is expected to be a busy transfer window at Anfield under new sporting director Jorg Schmadtke.
"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," Mac Allister added.
"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."
Liverpool boss Jurgen Klopp will aim to revamp a misfiring midfield after the departures of James Milner, Alex Oxlade-Chamberlain and Naby Keita at the end of their contracts.
After missing out on an unprecedented quadruple in the 2021-22 season, Liverpool will have to settle for Europa League football next season after ending a disappointing campaign in fifth place.
Liverpool were out of the Champions League and both domestic cups when they embarked on an 11-match unbeaten league run that included seven straight wins but finished outside the top four for the first time since 2016-17.