The Sharks also announced Tuesday they claimed forward Kyle Wellwood.
"We didn't give up anything off our team, so the addition just adds to the pool of players," general manager Doug Wilson said.
The additions come at a good time for the Sharks, who lost forward Scott Nichol to a four-game suspension Tuesday for hitting Phoenix defenseman David Schlemko in the head. Nichol will forfeit $16,344.08 in salary for the suspension.
The 27-year-old Eager has played in 34 games with Atlanta this season, posting three goals, seven assists, a plus-four rating and 77 penalty minutes. He was dealt after completing a four-game suspension without pay for punching Toronto's Colby Armstrong.
Eager was with the Stanley Cup champion Chicago Blackhawks last season. He has also played with Philadelphia.
"Ben Eager is a very engaged player," Wilson said. "The best compliment I can give him is he is like a big Scott Nichol. He can play the game. He's got speed and other teams are uncomfortable when he is out there. He's pretty valuable. He's gained valuable experience the last couple of years that can help our group."
Wellwood, 27, has spent this season playing in Russia, recording five goals and three assists in 25 games. Last season with Vancouver, Wellwood posted 14 goals and 11 assists in 75 games.
"He's played all year, he played in the KHL, so this is not a player who has been on the sidelines," Wilson said. "People come in and are given opportunities and we've seen that when players are given that opportunity, they will go the extra mile. There is no risk to us in this situation. It should be an exciting opportunity for him to showcase what he can do."
The Sharks also assigned forwards Andrew Desjardins and Brandon Mashinter, and defenseman Justin Braun to Worcester of the American Hockey League. They also activated forward John McCarthy from injured reserve.