The Perth-based Force, who had sacked coach Richard Graham in mid-April, finished second from last in the 15-team Super Rugby standings in 2012 with only three wins.
They were dealt a further blow last week when they lost Wallabies captain David Pocock to the Brumbies after a seven-year association.
The 45-year-old Foley will have to lift the side after joining the Force on a three-year contract.
"This is an important period for the club and while we're not looking to start from scratch, we're looking to re-launch the team," Foley said on the Force website.
"There's no doubt the club has had a few setbacks in recent times but there are many people at the club, both on and off the field, that are very determined to see the Force successful.
"While my expectations are realistic, I'm very excited about this challenge."
Foley spent three seasons at the Waratahs as assistant coach before taking on the head coach's role for the 2012 season. He resigned from his post on Tuesday.