Holmstrom will make $600,000 if he's on the NHL roster or $200,000 in the American Hockey League. The 27-year-old has seven games of NHL experience, including five in 2011-12.
He signed as an undrafted college free agent with the Philadelphia Flyers in 2010, and has played 256 games for the Adirondack Phantoms in the American Hockey League. Holmstrom had 13 goals, 32 points and 146 penalty minutes in 75 games for the Phantoms last season.
"Ben has served as Adirondack’s team captain and brings more veteran leadership to our system,” Carolina general manager Ron Francis said in a statement.