The combined fee for both players has been reported at an estimated £35m.
"I'm very happy to sign for Fulham, this is a big club that's very popular," Le Marchand, who can operate as a left-back or centre-back, told his new team's official website.
"I'm also happy to have joined up with a good friend, Jean Michaël Seri. I know that there is a lot of hard work ahead and I hope to bring my very best to this team," he added.
"I'm very pleased that we've agreed to a transfer for defender Maxime Le Marchand from Nice," Fulham director Tony Khan commented.
I’m very pleased that @FulhamFC has agreed to a transfer for defender Maxime Le Marchand from Nice. Strengthening our squad is always a priority and we've done a lot of work on Maxime and believe that his skills and versatility will be valuable assets to our Club. Come on Fulham! pic.twitter.com/lRY6dJovvh— Tony Khan (@TonyKhan) July 12, 2018
"Strengthening our squad is always a priority. In that spirit, we've done a lot of work on Maxime and believe that his skills and versatility will be valuable assets. Come on Fulham!"
Le Marchand started his career in the famed Rennes youth academy, before getting his senior break at Ligue 2 side Le Havre where he played alongside new £60m Manchester City winger Riyad Mahrez.
He joined Nice in 2015, playing in a top flight league for the first time in his career.