Cahill, who has previously coached Andre Agassi and Lleyton Hewitt, will begin his association with Federer at the Indian Wells this week, reports The Australian.
Cahill and Federer, who has been off the circuit for six weeks with a back injury, have been working together in Dubai, where the Swiss star has a base.
Federer has previously worked with other Australian coaches Peter Carter, who passed away in 2002, and Tony Roche.
Federer's agent Tony Godsick confirmed Cahill will guide Federer initially in his comeback but would not say how long the two would work together.
The Swiss maestro hasn't played since losing to Rafael Nadal in the Australian Open final in Jan.
Federer has won three successive Indian Wells titles, the last in 2006.