The 25-year-old joins Minnesota after spending the past six seasons with Norwegian side Molde. Gatt has earned two U.S. national team caps, but none since 2013.
The speedy attacker has been derailed by knee injuries in recent years, having undergone three surgeries.
"Josh has been on the American soccer radar for years," Minnesota sporting director Manny Lagos said in a news release. "He's a young player who left for Europe to build his career. He's had some really good moments, and a couple of tough injuries. But I think this situation lines up perfectly, in regards to where Josh is as a player, and what we're doing as a club."
A University of Michigan product, Gatt began his professional career with Austrian club SC Rheindorf Altach in 2010.
He joins a Minnesota attack boasting no shortage of wide options, with Kevin Molino, Miguel Ibarra, Johan Venegas and Bashkim Kadrii among the players competing for minutes on the flank.
"I've played my whole career as a pro in Europe," Gatt said. "To come back home, it's a nice revamp. It's nice to be able to do what I love in a setting I've grown up in. Playing overseas is different in every way. Playing here, there's a simplicity to it."