Dempsey joins a Fulham team second from bottom of the table and clearly hopes to be part of a squad that will improve under Rene Meulensteen.
The looming World Cup in Brazil - where he will guide the United States - was also a consideration.
In an interview aired on Fulham's official website, he said: "It feels good to be back.
"This has always felt like my home in Europe.
"I am excited to be back and be a part of this team and play in this league."
Of his reasons for returning, Dempsey added: "A lot of different things.
"I just wanted to be back playing at the highest level, get back to top form and get back to helping the team where they are not where they want to be in the table.
"Going into World Cup year you want to get to that top form and carry that forward, so hopefully have a good showing."