The 20-year-old Norway under-21s stopper arrives at the club for an undisclosed fee as a replacement for the outgoing Kiko Casilla who has joined La Liga side Elche on a season-long loan.
Klaesson - who has signed a four-year deal - follows Junior Firpo in being a new face for United's first team squad this summer.
First team winger and former Whites loanee Jack Harrison has also joined on a permanent deal from Manchester City this summer in which Lewis Bate, Sean McGurk and Amari Miller have also been signed, initially to link up with the under-23s.
Leeds United ‘would have taken’ four points from two games according to Alan Shearer
Leeds United U21 vs Norwich City U21 LIVE: match updates and team news from Thorp Arch
Rodrigo makes 'sleeping' Leeds United admission and declares action plan after Whites punishment
Leeds United in ‘talks’ with MLS star as Man Utd eye deal for Whites goalkeeper
Leeds United ‘have not’ approached pair but in transfer ‘talks’
A message from the Editor:
Leeds has a fantastic story to tell - and the Yorkshire Evening Post has been rooted firmly at the heart of telling the stories of our city since 1890.
We believe in ourselves and hope you believe in us too. We need your support to help ensure we can continue to be at the heart of life in Leeds.
Subscribe to our website and enjoy unlimited access to local news and information online and on our app.
With a digital subscription, you can read more than 5 articles, see fewer ads, enjoy faster load times, and get access to exclusive newsletters and content.
Click here to subscribe.
For more details on our newspaper subscription offers click here.
Thank you Laura Collins