The 23-year-old has signed until the end of August 2030.
"Malmö FF is a big club in Scandinavia with high ambitions, a clear goal and an attitude that I really like," he tells the club's website.
"I've spoken to a lot of people in and around the club and everyone has only had positive things to say. It's given me a really good feeling and I feel like this is an environment where I can thrive and develop."
Lahdo left Hammarby to join Dutch side AZ Alkmaar. He has been on loan to Nantes and Brøndby over the past year.
