Wirtz moves to the Premier League champions for an upfront fee of £100 million plus £16 million in potential add-ons.
The deal smashes Liverpool's previous record transfer, which was for forward Darwin Nunez from Benfica in 2022.
It could also eclipse the British mark of £115 million set by Chelsea in 2023 for Moises Caicedo if the add-ons are achieved.
“I feel very happy and very proud. Finally it’s done and I was waiting for a long time – finally it’s done and I am really happy," Wirtz told Liverpool.com.
“I'm really excited to have a new adventure in front of me. This was also a big point of my thoughts: that I want to have something completely new, to go out of the Bundesliga and to join the Premier League.
“I will see how I can perform there. I hope I can do my best. I spoke also with some players who played there and they told me that it’s perfect for me and every pitch is perfect, you can enjoy every game. I’m really looking forward to playing my first game.”
Wirtz made his debut for Leverkusen aged 17 and has since blossomed into a fully fledged superstar.
In the most recent campaign, he registered 16 goals and 15 assists as Leverkusen finished second in the Bundesliga and reached the Champions League last 16.
Wirtz was critical to the side in 2023/24 under Xabi Alonso as they won the Bundesliga title for the first time in their history.
He tallied 18 goals and 20 assists across 49 games in all competitions during that campaign and was named the Bundesliga Player of the Season.
Wirtz also has 31 caps to his name for Germany, recording seven goals since making his debut in 2021.
“I would like to win everything every year! First of all, we have to do our work, I have to make my work," he added.
“In the end, we want to be successful. Last season they won the Premier League so my goal is for sure to win it again and also to go further in the Champions League. I’m really ambitious.”
Wirtz is Liverpool's second signing of the summer from Leverkusen, with full-back Jeremie Frimpong arriving earlier on.