Liverpool have paid an initial £64m fee to sign the Uruguayan for the next six seasons.
Nunez scored 48 goals in 85 appearances for Benfica after joining from Almeria in September 2020, including one in each leg against Liverpool in the UEFA Champions League quarterfinals last season when Klopp saw his talent first-hand.
Having beaten the likes of Manchester United and Newcastle United to Nunez's signature, Klopp has been left delighted by getting the deal over the line.
"Darwin is a wonderful player, already really good but so much potential to get even better," Klopp told Liverpool's official website. "That’s why it's so exciting, to be honest. His age, his desire, his hunger to be even better than he currently is. His belief in our project and what we are looking to do as a club.
"He is as excited by us as we are by him, which makes for a great relationship, when you appreciate each other’s strengths. That is certainly the case here. He thinks we suit him and we believe he is the right fit for us.
"He has all the pieces we look for. He can set a tempo, he brings energy, he can threaten space from central and wide areas. He is aggressive and dynamic with his movement. He plays without fear, he's powerful. I know he will excite our supporters.
"It’s important we all recognise we are getting a 'work in progress' with Darwin. He recognises that himself, for sure. I love how much focus and humility he has.
"We have wonderful attacking options already and he becomes part of that now. So there is no pressure on him at all. He signs for a very long time and we intend to nurture his talent and see it grow."
