Origi joined the Reds from French Ligue 1 club Lille following an impressive showing at the 2014 FIFA World Cup for Belgium, but was immediately loaned back to Les Dogues for the 2014/15 campaign.
The 20-year-old will now join the Merseysiders ahead of the upcoming season and his international team-mate Mignolet has no doubt his young compatriot has all the tools to be a hit in England.
“He’s only young but on the other side he’s also quite experienced, having played in Ligue 1 in France and with the Belgian national team,” he told the official Liverpool magazine.
“He’s got a lot of ability, he is quick and can score a goal and he is willing to work for the team and put pressure on defences.
“He’s got a great attitude, so what more do you want? I am looking forward to when he is going to join.”