"I thought they were trying to reduce the deficit in Washington," new Mets general manager Sandy Alderson said.
The 31-year-old Werth, who helped the Phillies win the 2008 World Series title, hit .296 this year in his fourth and final season with Philadelphia. He had an NL-high 46 doubles, 27 homers and 85 RBIs.
His agreement was announced two days after the Nationals' cleanup hitter, Adam Dunn, left for a $56 million, four-year contract with the Chicago White Sox.
"We took some light criticism about Adam Dunn leaving," Nationals manager Jim Riggleman said, speaking in the news conference room after the announcement. "People said it was the money. But it's not about the money, as this deal shows. We gave Jayson Werth more."
Werth's contract matched the 12th-largest among current players, a huge deal for a player with only one All-Star selection to his credit. And coming relatively early in the free-agent market, it could have a trickle-down for others seeking new deals.
"Makes some of our contracts look pretty good," said Alderson, whose Mets have been saddled with high-priced, underperforming players. "It's a long time and a lot of money."
Werth moves from the team that has won four straight NL East titles to one that finished last this year at 69-93 and hasn't had a winning record since 2003 - the franchise's next-to-last season as the Montreal Expos.
"It kind of exemplifies phase two of the Washington Nationals' process," general manager Mike Rizzo said. "Phase one was scouting and player development, building the farm system. ... Now it's the time to go to the second phase and really compete for division titles and championships."
Werth's deal was negotiated by agent Scott Boras, who also negotiated big-money agreements with the Nationals for the last two No. 1 picks in the amateur draft, pitcher Stephen Strasburg in 2009 and catcher-outfielder Bryce Harper this year.
"We think he's going to be a big piece of the puzzle," Rizzo said. "We certainly have more holes to fill. We had more work to do, and we're certainly aggressively going on from here and beyond."
Boras said talks began just before Thanksgiving when Nationals owners Ted Lerner and Mark Lerner met with Werth at Boras' office in Newport Beach, Calif. The sides reached a preliminary agreement Friday.
Familiarity from the previous deals helped.
"The Lerners and I don't share Thanksgiving dinner, but we've shared a lot of dinners lately. That's for sure," Boras said.
As the Nationals hope to become competitive, Boras said Werth is only an early step. He compared it to when the Detroit Tigers negotiated a deal with him for Ivan Rodriguez, then added Magglio Ordonez and Kenny Rogers from his clients in later years.
"To change the perception of your franchise, you're going to have to win, and once you do win, you're going to have to continue to win, and that's a hard thing to do in the National League East when you have a couple of Goliaths there," Boras said. "The question is: Do you want to be a Goliath along with the two you have and maybe another couple teams that are on their way to taking those steps to be that?"
Werth played for Toronto (2002-03) and the Los Angeles Dodgers (2004-05) before becoming an All-Star with the Phillies in 2009.
"For Jayson this was a decision where he certainly wanted to know that this was place that was not only going to take every step possible to sign young players in the draft, as they've exhibited, but also take steps a core system in the minor leagues and also take further steps and advance in the free-agent process so that he could be surrounded by quality major leaguers in addition to those already present in the Nationals organization."
Nationals manager Jim Riggleman, who didn't know the deal had been finalized until just before it was announced. was the Dodgers bench coach while Werth played for Los Angeles.
"We got the inside scoop on who the man is and who the person is," Rizzo said. "Jim is a great judge of character and clubhouse presence. He was very flowery in his praise in Jayson on and off the field. He feels, like I feel, Jayson's best days haven't been had yet.
Werth is the grandson of Ducky Schofield and nephew of Dick Schofield, a minor league teammate of Rizzo. In addition, Rizzo has scouted Werth since he played high-school ball.
"I've been a fan of his lineage and his family," Rizzo said.
AP Baseball Writer Ben Walker contributed to this report.