Ottawa gets a conditional second-round pick and Ryan Potulny from Chicago in exchange for Campoli and a conditional seventh-round pick.
"I'm extremely excited to join their team," Campoli said on a conference call. Blackhawks general manager Stan Bowman said the Canadian needed his U.S. work visa and was expected to join the team after Monday's game at Minnesota.
"I think there are so many positives in the situation for me," Campoli said. "I'm a puck-moving, up-ice-often defenseman. Skating's a big part of my game, and I know from playing against Chicago, they're a team that's a puck-possession, aggressive, up-tempo style team, and I really think there's a fit there so I'm pretty excited about the whole thing right now."
The need for a defenseman became more critical because Jordan Hendry tore his ACL.
Hendry, 27, left Sunday's game against the Phoenix Coyotes after getting checked into the end boards by forward Shane Doan. Hendry was helped off the ice and into the dressing room without putting any weight on his left leg.
"Jordan injured his left knee last night during a collision into the boards and has sustained an ACL tear," Blackhawks team physician Michael Terry said in a statement. "He will undergo reconstructive surgery shortly and we anticipate a full recovery in approximately six months."
Hendry, a healthy scratch for part of the year, had played in nine consecutive games, moving ahead of the now-departed Nick Boynton on the depth chart.
Bowman said he's not sure when Campoli will join the Blackhawks.
"We're hoping he'll get here as soon as he can," Bowman said. "Canadian player in a Canadian city, he doesn't have a U.S. working visa. Hopefully getting that done in short order. In some ways it's out of our hands. We're doing all we can to expedite things. He's certainly ready to go, he's healthy."
Bowman had said that he was looking for help on defense before Monday's trade deadline.
Campoli, a six-year veteran, has three goals and 11 assists and is a minus-3 this year.
He is the sixth regular player in the Senators lineup to be traded in the past three weeks. Alex Kovalev, Mike Fisher, Chris Kelly, Jarkko Ruutu and Brian Elliott also were dealt by Ottawa, the last-place team in the Eastern Conference.
"I think the good news for Chris is that he's coming into a situation here where he's not going to be required to carry the load," Bowman said. "We've got a lot of guys that can play good minutes, so he needs to complement them, and I think in some ways, he's going to alleviate their load. I think his skill set and his experience is going to be a nice addition to our club. I think it's a definite upgrade."
Campoli joins a team that has been inconsistent all season and is struggling to make the playoffs after winning the Stanley Cup last season.
"I know this," Campoli said. "I know they're a great team. They're right in the thick of things in the West. What I like about the situation is they're an upbeat, up-tempo, high-energy [team]. They're for the most part a young group. The core of the team is a young group. I'm really excited to be a part of that."
Potulny has been bounced between Chicago and Rockford of the AHL this season. In three games with the Blackhawks, the center has no points. He had 18 goals and 23 assists in 58 games with Rockford.
The Senators did keep one key player in defenseman Chris Phillips, who has played all 925 of his NHL games with the Senators agreed to a $9.25 million, three-year contract extension.
Phillips chose not to explore free agency on July 1.
"There's no question that I gave up something," he said. "But what that is we'll never know because I didn't go to July 1 and test that market. It's not a concern."
"Phillips has been around here for a long time, he's a great leader in the room and a guy that a lot of guys lean on so we're happy to see him stay," Senators forward Jason Spezza said.
"I think it's been trade deadline day for a few weeks for us now so not much has changed."
Pierre LeBrun covers the NHL for ESPN.com. Jesse Rogers covers the Blackhawks for ESPNChicago.com. Information from The Associated Press was used in this report.