The 26-year-old defender moves to Dingwall from Houston Dynamo on a free transfer, having spent four years in Major League Soccer.
"Andre was a very good signing for us when we brought him here in 2009. He had four very good years here, was on three play-off teams," said Dynamos president Chris Canetti.
"He was a very nice player for us, a great person, excellent in the community and we're glad to have had him and are sorry to have lost him. We wish him the best in the future."
Hainault has 32 caps for his country having made his debut against Hungary in 2006.
He joins Ivan Sproule in Easter Ross, while Adams has said he is looking to add one more face before the end of the month.
"We're working on a foreign deal for a player from Greece and we're just waiting on international clearance," he said.