Victorino, who is on a snorkeling trip in Maui, confirmed on his Twitter account that he has joined the rapidly rebuilding Red Sox.
"Just agreed to join the Boston (at)RedSox in the middle of paradise," Victorino tweeted. "(hash)BLESSED!!! Can't wait to get to Boston!"
The deal, pending a physical, is worth $39 million over three years, according to a source with direct knowledge of the negotiations.
The terms of the agreement are exactly the same as the deal Boston reached with free-agent first baseman/catcher Mike Napoli on Monday.
Victorino, a three-time Gold Glove winner, is a natural center fielder with a limited number of games (148) in right field. With Jacoby Ellsbury in center, he projects as the team's everyday right fielder.
Red Sox manager John Farrell indicated that whoever plays right field for Boston will need the defensive skills to handle the position.
"It's probably the toughest right field in baseball to play, just in terms of the space to cover," Farrell said. "So that range comes into play, and yet you try to combine the best range available with some offensive production.
"It might not be your prototypical type of right fielder where it's a power bat, because we do value the defense in that area. That's not to exclude anyone, but defense takes a high priority in that position at Fenway."
Red Sox general manager Ben Cherington was asked how comfortable he is with a non-prototypical right fielder playing right field.
"In our ballpark, we'd like to have someone who's played a lot of center in right field," Cherington said. "There are guys out there who have done both. If you've played a lot of center field and have played in different parks, then it may be a little bit of an adjustment. But you can figure out right field at Fenway."
Cherington did not rule out re-signing outfielder Cody Ross, and said dialogue between the sides hasn't closed.
"Obviously, I don't want to say too much about the specific nature of the conversations (with Ross), because they go back a ways," Cherington said. "As of now, we haven't been able to find something that makes sense, but the door is still open. We'll see what else happens. Again, he's got other options, too.
"We talked during the season and right after the season. Then we've talked since then, but obviously we weren't able to reach an agreement earlier in the process. ... We've kept the dialogue going, kept the door open, but it just hasn't culminated into anything yet."
Victorino's ability to play center field likely was important to the Red Sox. Ellsbury is eligible to become a free agent after the 2013 season and certainly will be looking for a major payday, especially with Scott Boras as his agent.
Having Victorino locked up for the next three years will allow the Red Sox to move him to center field if Ellsbury signs elsewhere or if the team decides to trade him before that. It also gives the Red Sox time to wait for outfield prospects Ryan Kalish, Jackie Bradley Jr. and Bryce Brentz to be ready to contribute in the majors.
Cherington stressed the importance of having flexibility.
"(Signing Victorino is) not related; it wouldn't be related specifically to any other potential move," Cherington said. "But generally, everything we're trying to do this offseason has sort of a short-end, long-term reason and hopefully fits into the -- I don't want to say our five-year plan because that's too far out -- but medium-term plan."
ESPNBoston.com's Joe McDonald and The Associated Press contributed to this report.