The Seahawks swapped the 40th pick in the second round with San Diego's 60th pick and also will send the Chargers a third-round pick in the 2011 draft.
Seattle, meanwhile, has signed Whitehurst to a two-year, $8 million contract, with $2 million more in incentives, sources said.
New coach Pete Carroll said he is excited about Whitehurst's potential.
"We are all about competition," Carroll said. "Charlie has tremendous talent and upside and we are very excited to watch him develop and help our football team."
Whitehurst, a restricted free agent with third-round compensation, has had only four NFL snaps and has not thrown a pass in a regular-season game. The Clemson product signed his one-year restricted tender Wednesday, which facilitated the trade, after deciding he preferred to play in Seattle instead of Arizona.
"I haven't played four seasons in the NFL, but I've been behind a great quarterback in Philip Rivers," said Whitehurst, son of former NFL QB David Whitehurst. "It's a similar situation to Matt here. You learn a ton from those guys.
"I think I can move a little bit. I think I can make the throws. I think I can lead the team and think we can win. I certainly have some things to work on. I don't have a ton of experience in game situations. I understand that. That's where I have to make up pretty soon and convince everybody this was the right thing to do. That's what I plan on doing."
Matt Hasselbeck, 34, remains Seattle's starting quarterback, but the 27-year-old Whitehurst could be viewed as the quarterback for the future.
This is the first major decision for new general manager John Schneider, who was hired Jan. 19 to turn around a franchise that has had a 9-23 record over the past two seasons.
"When you see something like this available," Schneider said, "you have to take your shot."
He said the Seahawks "would consider Charlie part of our draft class" but didn't rule out drafting another quarterback this year. The Seahawks hold two first-round selections, the sixth and 14th.
Carroll, who replaced head coach Jim Mora in January, said "for our situation, we think we're getting a guy ahead of a college guy coming out.
"He certainly has not been on the football field but he's in those meeting rooms, on the practice field, he's in on the strategy on game day. All those things add up," Carroll said. "There's always risk involved when you make decisions like this. But our research and our background in making a trade of this nature, we felt he had the elements put together in a process that allows us to make a confident, solid decision. We're not looking over our shoulder on this deal."
Adam Schefter is ESPN's NFL Insider. John Clayton is a senior NFL writer for ESPN.com. Information from The Associated Press was used in this report.