"I will feel like a kid at a new school. I'm so excited to join the team, and really be challenged," Folau said.
"It will be a new team, new dynamics, new playing styles, so this is a real game-changer for me to challenge myself and play the best netball that I can."
Thunderbirds new head coach, Tania Obst, said Folau would bring a wealth of experience and a world-class quality to the team.
"What a fantastic signing for our club, members and supporters for the 2019 season," Obst said.
"The contribution she will make to our attacking end will be significant as well as the added value of working with our two young SA shooters.
"For the Club, it sets us solidly on the path for long-term sustainability and success. Maria is an incredible player, a superior athlete and sets the Adelaide Thunderbirds up for a strong, successful and competitive season."
Folau will join a promising Thunderbirds line-up with Commonwealth Games gold medallists Beth Cobden and Layla Guscoth, who both lined up for the Roses throughout the recent international season, also recently signing with the franchise.
Folau will meet with the Thunderbirds' players and the off-court team in November when they start to work towards pre-season.
The Thunderbirds finished last on the Super Netball ladder this season with four points after a loss to the New South Wales Swifts 69-41 in their final game.