MINNEAPOLIS -- The Twins officially made their first major upgrade to their rotation on Tuesday, as they welcomed right-hander Ricky Nolasco to Minnesota in a news conference at Target Field.

Having passed his physical on Monday, Nolasco inked a four-year deal worth $12 million annually with a club option that could vest in 2018. The $48 million pact is the largest free-agent signing in the club's history, surpassing Josh Willingham's three-year, $21 million deal signed before the 2012 season.

"This is a good day for the Minnesota Twins," Twins general manager Terry Ryan said. "As everybody knows, we've had some issues on the mound, particularly in the starting rotation, and we set out this fall to improve our ability to compete. So when Ricky filed for free agency on Nov. 2 or so, he was one of the guys we pinpointed to bring over here, and we did just that."

Nolasco, who turns 31 on Dec. 13, is a major addition to a rotation that finished with the worst ERA in the Majors last season. Nolasco posted a 3.70 ERA with 165 strikeouts and 46 walks in 199 1/3 innings with the Marlins and Dodgers last season.

Nolasco said he was impressed by how aggressive the Twins were in free agency and believes he can help turn around a franchise that has experienced three straight seasons with 95 or more losses.

"Them making me feel so wanted here was probably the biggest factor," said Nolasco, who changed his Twitter avatar to a Twins logo shortly after news broke that he had agreed to sign with the Twins on Wednesday afternoon. "They reached out to us on Day 1 and never slowed down. It's a good feeling to have someone come after you like that and feel wanted. So I'm happy to be here."

He was a solid addition for the Dodgers down the stretch after being acquired in a trade with Miami on July 6, as he posted a 3.52 ERA in 16 appearances. He also made one start in the National League Championship Series against the Cardinals, giving up three runs over four innings.

Nolasco is known for his durability, averaging 31 starts per season over the last six years. He's made at least 30 starts in five of the last six seasons, missing the mark in '10, when he made just 26 starts because of surgery to repair the meniscus in his right knee. He hasn't been on the disabled list since that season.

Nolasco has a career 89-75 record with a 4.37 ERA in 229 career appearances, including 212 starts. He's struck out 7.4 batters per nine innings over his career, which was his exact mark in '13, as well. He also has walked just 2.1 batters per nine innings throughout his career.

"He has a lot of ability," Ryan said. "He can strike people out. He doesn't walk people. He competes. He's very dependable. He pounds out innings. And also his character and the way he is as a teammate all adds up to what we were looking for."

The Corona, Calif., native was originally drafted by the Cubs in the fourth round of the 2001 First-Year Player Draft, but was traded to the Marlins before the 2006 season.

He's represented by agent Matt Sosnick, who was also present at the press conference. Nolasco said the fact the Twins were willing to go four years with an option was a major factor in his decision. Nolasco's contract has a $13 million option with a $1 million buyout. The option can vest if he throws a combined 400 innings between 2016-17.

"I think the vesting on the fifth was even bigger for us to turn this into a possible five," Nolascco said. "The way I look at it is it's a five-year contract for me. I have no issues with my body and feel great. I believe 100 percent in myself that I am going to fulfill all five years of the contract."

The Twins have one more signing to announce this week, as they've yet to officially sign free-agent right-hander Phil Hughes, who agreed to terms on a three-year deal worth $24 million on Saturday. But it's expected to come as soon as Thursday, and Ryan indicated more signings could be on the way.

"We are not done in this free-agent issue," Ryan said. "We still have a few more things we'd like to pursue and have gotten close to. If we can the pitching staff on this ballclub straightened out, it can help us in a lot of ways."