The 26-year-old Portugal international has agreed a five-year deal, with an option for an additional 12 months, keeping him at Craven Cottage until at least the summer of 2027.
Speaking to FFCtv, Palhinha said: “I'm very glad to be here. It's a big opportunity for me, for my career, to play in what is – in my opinion – the best league in the world.
“I've signed with a great Club. The Club wanted me, and I chose the Club, so I promise the fans that I will do my best, and I hope we can win so many things in this season."
João Palhinha poses in the First Team changing room after signing
Cottagers chief Tony Khan added: “João Palhinha has excelled in Portugal playing both club and international football. He's been one of our top targets in this window.
“While there were other prominent clubs aiming to secure his signature, we're thrilled that João chose to come here and that he wants to play for Fulham under our great coach Marco Silva, and we believe that João will be a valuable addition to strengthen the squad to compete this season in the Premier League.
“Come on Fulham!"