Annacone has worked with Pete Sampras and Tim Henman in the past
Roger Federer has hired Paul Annacone as his coach on a full-time basis after a successful one-month trial period.
A statement on Federer's website said Annacone will work with him during the 2010 US Open and "going forward".
Annacone is scheduled to quit his role as Lawn Tennis Association head coach in November.
Federer, who has slipped from second to third in the world rankings in 2010, is aiming for his 17th Grand Slam title at the US Open, which starts on Monday.
Five-time champion Federer, who lost to Juan Martin del Potro in the 2009 final, will meet Argentine Brian Dabul in the first round at Flushing Meadows.
Federer's last two Grand Slams - the French Open and, most recently, Wimbledon - have uncharacteristically ended at the quarter-final stage, resulting in his lowest ranking for seven years.
However, the world number two from Switzerland looked to be returning to something like his best form when he won first title since January's Australian Open at the Cincinnati Masters, beating Mardy Fish in the final.
Federer added in his statement: "Paul and I have had a good trial period... he [Paul] will be integrated more and more as his responsibilities with LTA wind down."
The LTA announced in May that Annacone would leave his post in November after three years with the organisation.
The 47-year-old American has previously worked with Pete Sampras, Tim Henman and Marat Safin.
Federer has had several temporary associations with coaches in recent years, including Darren Cahill, Jose Higueras and Tony Roche, but has also gone without a coach for extended periods.