Ratten is the Senior Coach at St Kilda Football Club.
He spent the past six years at Hawthorn as an assistant under Alastair Clarkson, after six years as Carlton senior coach from 2007-2012.
General Manager of Football Simon Lethlean said Ratten’s experience would be an important asset to the Saints as the club looks to respond to a disappointing 2018 season.
“Brett is one of the most experienced assistant coaches in the game and we look forward to the impact he can have on our football program,” Lethlean said.
“He is highly regarded across the football industry and as midfield coach at the Hawks, was a key driver in their premiership success.”