Timonen, who will turn 40 on March 18, has not played this season after doctors discovered blood clots in his lower right leg and in both lungs. He has been cleared for contact.
"Obviously this last summer when I got sick, I was back in Finland in a hospital bed, and they said you have to wait six months to see what's going to happen," Timonen told reporters on a conference call Friday night. "Obviously I was asking a lot of questions about my career and can I still return playing hockey. [The specialists] said, 'Well, you have to eat this medicine for six months, then you have a small chance to get back on the ice. So in that moment, I decided if that small chances happen the only thing I'm missing from hockey career is a Stanley Cup.
"That was the only goal which I would return to hockey. It wasn't money. It wasn't anything else that was missing.
"I'm really excited about joining the Chicago team. ... It's been a tough couple days. I always wanted to retire [in Philadelphia]. Again, my goal was to win the Stanley Cup and get into the playoffs. I feel like this was the right move.
Timonen, who began practicing a few weeks ago, will arrive in Chicago on Saturday and will practice with the team Sunday. He is unsure if he will play in the Blackhawks' next game on Monday.
"It's going to take a few days [to get into game shape]," he said. "I don't have a exhibition game to kind of easy myself into it. I have to be good to go right away, and I have to feel 100 percent. I feel really good right now."
When asked when he expects Timonen to play, coach Joel Quenneville said the plan is "right away."
Timonen began having conversations with the Flyers about his future several weeks ago. The Flyers' playoff hopes appeared slim then, and Timonen said he would be OK with a trade if it gave him a chance to win a Stanley Cup. Chicago-based Markus Lehto, who has been Timonen's agent for 20-plus years, said the Flyers were respectful of Timonen and cleared the trade with him before making it.
"We've been working on this one for a while," said Blackhawks general manager Stan Bowman, who is with the team in Tampa Bay -- Chicago lost to the Lightning, 4-0, on Friday night. "He was a defenseman we really wanted. Setting aside the fact he hasn't played, once we get him up to speed, he's a great player. He's been an elite defenseman for a lot of years.
"We looked around at the other guys. When we get him back on his game, he's a great defenseman, low risk, high reward.
"I know he's older, but it's not like he's coming back from an injury. He didn't hurt his knee or his shoulder. He's obviously had the blood issue, but we're past that, so he's fresh. He's ready to go. Obviously he's going to be a little rusty.
"He's been skating, so I think he's ready to play in some games, and it will take him some time to get him to his peak level, but we've got six weeks to go until playoff time, so we're going to build up to that."
Timonen has said he will retire after the season.
His health problems occurred following a blocked shot, combined with a hereditary blood disorder. It has kept him off the ice throughout this season, and during his recovery he spoke with other players suffering the same malady.
"Somebody called me Dr. Timonen," he said. "The minimum was six months to be on blood thinners, and obviously I have a lot of time to really do some researching and see what's the deal with it."
Timonen, a left-handed shot, had six goals and 29 assists in 77 regular-season games for the Flyers last season. He ranks third among active defensemen with 571 career points in 1,092 games over 15 seasons.
"Obviously, he's had a pretty great career," Blackhawks defenseman Duncan Keith said. "He hasn't played a whole lot this year, but he's a smart D man and any time you can add a guy like that with experience, I think it's going to help. We're excited to have him, if that's the case."
Timonen has played in five Olympics for Finland and has appeared in 87 Stanley Cup playoff games.
The conditional fourth-round pick received by the Flyers could move up to as high as a second-rounder in 2016 if the Hawks win three playoff rounds and Timonen plays in 50 percent or more of those games, or if Timonen doesn't play at all in the first two rounds but plays 50 percent or more in the third round and the Hawks reach the Stanley Cup finals.
Bowman said Thursday he was close to making a trade and could be seeking to acquire a defenseman and/or a forward. On Friday he intimated the Blackhawks might not be done dealing before Monday's trade deadline.
"We're not done making calls. It's been a long day," Bowman said. "Like I said last night, you can't predict where it will go. It takes two sides to make a deal. We're going to keep trying."
The Blackhawks became more aggressive in the trade market when forward Patrick Kane suffered a fractured clavicle on Tuesday. He is expected to miss 12 weeks.
"We're still looking for a forward," Bowman said. "We'll see how it works out."
Chicago also placed defenseman Johnny Oduya on injured reserve Friday.
Information from the Associated Press, ESPN.com's Pierre LeBrun and ESPN.com contributor Chris Girandola was used in this report.