To make room on the 40-man roster, the Royals designated backup catcher George Kottaras for assignment. He batted .180 in 46 games this year.
The long-term commitment, Vargas said, came because he liked Kauffman Stadium, the friendly Kansas City fans and the recent improvement made by the team.
"What excites me about the team is how I've seen the team grow and progress a lot over the last four or five years," he said. "You know what they put out there is a great team, and their defense is spectacular. I just hope I can be a piece of the puzzle that helps move us forward."
Four years is also beyond the length that general manager Dayton Moore previously indicated he's comfortable giving to veteran players, but he said, "I think the most important thing is that our medical team felt very comfortable, our scouting judgment was very sound with the length of the contract as well. It all kind of lined up together."
The Royals faced the loss of two starting pitchers when right-hander Ervin Santana and left-hander Bruce Chen entered the free-agent market. That left only right-handers James Shields and Jeremy Guthrie as sure-fire starters for 2014. So Vargas, an eight-year veteran, provides needed experience that would be lost if Santana and Chen sign elsewhere. Santana probably priced himself out of the Royals' reach with reported expectations of a five-year deal at $100 million or more.
In fact, asked about Santana, Moore said: "It's probably a difficult maneuver for us at this point in time, but we'll stay engaged and see how that unfolds."
However, Moore did not rule out Chen's possible return. He also indicated the club is open to signing another starting pitcher.
As the roster now stands, others in the hunt for rotation jobs likely will include left-handers Danny Duffy and Will Smith and right-handers Wade Davis, Yordano Ventura and Kyle Zimmer. Luke Hochevar, who spent last season in the bullpen, is another possibility. Luis Mendoza dropped out of the picture when he signed to pitch in Japan.
It'll be up to manager Ned Yost to slot Vargas into the rotation, but, as a left-hander, a likely spot would be between righties Shields and Guthrie.
Vargas, 30, spent the 2013 season with the Angels, compiling a 9-8 record and a 4.02 ERA in 24 starts. He had three complete games and two shutouts. In 156 innings, he had 109 strikeouts and 46 walks. A blood clot discovered in his left armpit after a June 17 outing led to surgery on June 26, and he missed seven weeks. After his return on Aug. 13, he made 10 starts and went 3-4 with a 4.60 ERA.
"I'm 100 percent and ready to get after it. There's nothing lingering or any further things that need to take place," Vargas said.
Vargas was named the American League Pitcher of the Month last May, when he went 5-0 with a 2.30 ERA in six starts. Two of those victories were over the Royals, and, in fact, he's 6-1 in his career against them.
Vargas has seen enough of the Royals to know he'll like performing with their defense.
"I think any pitcher is excited about a really good defense, and three Gold Gloves says a whole lot," he said. "So getting a chance to come here and know I have an opportunity to be a part of something for the next four years and a chance to do something special here in Kansas City is the reason why I came."
The chance to pitch to All-Star catcher Salvador Perez is also appealing.
"I've only gotten a chance to see it from the other dugout, but he's one of the things that you definitely notice most out there on the field. Not only his presence but the way he's able to control the game, throw the ball and receive," Vargas said. "He's also a pretty imposing figure in the batter's box, so I'm definitely looking forward to getting to meet him, build a relationship and hopefully do some good things."
Vargas was obtained by the Angels prior to last season in the trade that sent designated hitter Kendrys Morales to the Seattle Mariners. He pitched four years for the Mariners after time with the New York Mets and the Florida Marlins. In eight Major League seasons, he's pitched 174 games, all but 20 of them starts, with a record of 51-58 and a 4.30 ERA. His biggest season came in 2012, when he led the Mariners in victories with a 14-11 record and had a 3.85 ERA in 33 starts. He worked 217 1/3 innings that season, his second straight year over the 200 mark.
That workhorse strain is something that appealed to the Royals.
"You want your starting rotation to be able to pitch 1,000 innings combined," Moore said. "It's a tall order, but you try to get 200 innings out of your starters, and Jason has been able to do that. He's been one of the more consistent pitchers in all of baseball the last few years."
His time with the Mets included just two games in two years. He spent most of 2007 in Triple-A and underwent elbow surgery after the season. He missed the entire 2008 season because of hip surgery, then was traded to the Mariners.
A product of Apple Valley, Calif., Vargas played at three colleges -- Louisiana State University, Cypress College and Long Beach State. He signed after being drafted in 2004's second round by the Marlins, and made his big league debut the next year.
He's worn several different uniform numbers in his career but never No. 51 as he displayed on his Royals jersey on Thursday.
"I looked at the numbers available and let my 3-year-old daughter pick, and 51 is what she picked," he said.