The Curbishley announcement came just hours after the Premier League club revealed attacking midfielder Dempsey was returning on a two-month loan from Seattle Sounders.
It has been a time of change recently at Craven Cottage with former manager Martin Jol sacked on December 1 to be immediately replaced by Rene Meulensteen.
Tuesday's arrivals of Curbishley and Dempsey will give the fans hope the club can start to improve on the field as they sit second from bottom at Christmas.
While Dempsey, 30, returns from Seattle Sounders in the Major League Soccer off-season, for Curbishley it is his first role at a club since leaving the Hammers in September 2008, despite being linked with many managerial vacancies.
A statement on Fulham's official website read: "With a wealth of football experience behind him, Alan will work with head coach Rene Meulensteen as the club embarks on the second half of the season, and the important task of securing our Barclays Premier League status for a 14th consecutive campaign.
"Both Curbishley and Meulensteen will report to the club's CEO Alistair Mackintosh."
Meulensteen said: "I'm very happy that Alan has joined us as I know his expertise will be invaluable as we enter the remaining months of the season.
"Following Martin [Jol's] departure I discussed with both Alistair Mackintosh and the chairman the challenges we face, and I was delighted that they supported the idea of additional support within the coaching team.
"Alan has a proven track record in the industry and understands full well what it takes to succeed. I look forward to sharing ideas and listening to advice, to ensure Fulham Football Club remains where it belongs: in the Premier League."
Dempsey, meanwhile, spent five and a half seasons at the West London club having first signed a permanent deal in January 2007 from New England Revolution.
In his first spell with Fulham Dempsey scored 60 goals in 225 appearances, among the most memorable was the fourth goal in a 4-1 win over Juventus in the Europa League which completed a comeback over two legs as they made their way to the final in 2010.
Dempsey also scored the only goal of the match against Liverpool at Craven Cottage in May 2007 which secured Premier League football for the club the following season.
He was voted Fulham's player of the season two years in a row, the last following the 2011/12 season after which he signed for Tottenham in August 2012.
Dempsey moved to North London in a £6million switch, despite having been heavily linked with Liverpool and Aston Villa, but he spent just a year at White Hart Lane before returning to the United States and the Seattle Sounders.
Dempsey joins a Fulham team second from bottom of the table and clearly hopes to be part of a squad that will improve under 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 a World Cup year you want to get to that top form and carry that forward, so hopefully have a good showing."