The Welsh outfit have revealed that Evans will leave Rodney Parade and join up with his new teammates at the end of the season.
"This is a great opportunity for me," Evans told the club's official website.
"The Ospreys have been the most successful team in Wales over the last 10 years, winning leagues and producing players for the national team.
"There is some real world-class talent in the squad, so it's a big challenge for me personally, but I can't wait to get involved and fight for my place."
The 25-year-old has earned two caps for Wales so far in his career.