Wirtz made his debut for Leverkusen at the age of 17, scoring 57 goals in 197 games for the club, and helped them win the Bundesliga for the first time in 2024.
He has scored seven goals in 31 appearances for Germany since making his international debut in 2021.
Wirtz is set to become the second player Liverpool have bought from Bayer Leverkusen this summer, with right full-back Jeremie Frimpong having arrived in a £34m deal.
The Reds have also made a move for Bournemouth left-back Milos Kerkez, with talks taking place about a deal of between £45m-£50m.
Liverpool, having won the 2024-25 Premier League title in manager Arne Slot’s first season, have sought to bolster their squad – and the level of their outlay is believed to have been helped by limiting their spending in previous transfer windows.
Last summer, they only added Italy winger Federico Chiesa, bought for £12.5m from Juventus, while Georgia goalkeeper Giorgi Mamardashvili was signed from Valencia in a £29m deal which will involve him joining before the start of next season.
In terms of departures, Liverpool have sold Republic of Ireland keeper Caoimhin Kelleher to Brentford for an initial £12.5m, which could rise to £18m.
They have also lost England right-back Trent Alexander-Arnold, who has joined Real Madrid.
Sources at Liverpool have indicated Real paid the Reds 10m euros (£8.4m) to release Alexander-Arnold early from his contract, which was scheduled to end on 30 June, so he could play at this month’s Club World Cup, although sources at the Spanish club have suggested they paid less than that.