After four years at the Emirates, Leno has decided to swap North for West London in search of regular first-team football in his bid to be named in Germany's World Cup squad for Qatar.
Leno has put pen to paper on a contract until 2025, with the option of a further 12 months.
Speaking to Fulham's website, he said: "It feels amazing to finally be here.
"I can’t wait to join the team, to train and play with the team.
“I’m relieved that everything is done. I’m just happy to be here.
"It took a little bit of time but in the end we made it, and that’s the most important thing.”
Fulham co-owner Tony Khan added: "Bernd Leno is the goalkeeper whom we have pursued steadfastly throughout this transfer window, and we’re very excited that we’ve reached a transfer agreement and he’s now fully committed to Fulham!
“He has played at the highest level, and he’ll bring this experience and his leadership to our team.
"He’ll be a great addition to Marco’s squad, who are all excited for the season ahead! Come on Fulham!”
Arsenal were quick to thank Leno for his service after 125 games played.
A club statement read: "We thank you Bernd for your contribution to the club during your four years with us.
"Everyone at Arsenal wishes Bernd and his family all the very best in their new chapter.
Posting a message to Gunners supporters on Twitter, Leno said:
"It’s been a pleasure to be part of this great football club for four amazing years. Thank you very much for your support.
"Also a big thank you to my team-mates and the staff behind the team. I‘m looking forward to see you soon!"