Sherrill agreed to the $1.1 million deal the week before Christmas, but didn't get to Seattle for his physical until after the holiday as he and his wife were caring for their newborn son.
"It's good to have everything done and know for sure what's going on," Sherrill said after returning to his home in Salt Lake City.
With the contract official, general manager Jack Zduriencik can cross left-handed bullpen help off his wish list after adding one of baseball's better southpaw specialists. Sherrill, 34, has held left-handed hitters to a .180 batting average with a .515 OPS in 550 career at-bats.
Since 1974, B.J. Ryan is the only lefty in baseball with a lower batting average against by left-handed hitters (with a minimum of 500 at-bats) than Sherrill at .179. Billy Wagner is third with a .190 average.
Sherrill went 3-1 with a 3.00 ERA in 36 innings over 51 appearances last season for the Braves, with 38 strikeouts and 12 walks. He had 32 strikeouts and just one walk against left-handed hitters in 78 at-bats.
Sherrill originally broke into the Majors with the Mariners in 2004 after being signed out of the independent leagues. He went 10-8 with a 3.65 ERA in 195 appearances during four seasons with Seattle before being included in the Erik Bedard trade to Baltimore.
"It's nice to bring a guy back home, as it were, but more than anything, he fit what we were looking for," Zduriencik said. "He's a veteran guy who can get left-handers out. He's excited about his return, but this is more about what he can help us do with winning games. He's a veteran who is well thought of as person and competitor."
Sherrill said it seems like 20 years since he was dealt to the Orioles by former GM Bill Bavasi along with outfielder Adam Jones and pitchers Kam Mickolio and Chris Tillman on Feb. 8, 2008.
"That was just one of those things with Bavasi pretty much knowing he needed to win right away and just trying to do whatever he could to accomplish that," Sherrill said. "So definitely no hard feelings. It should be a lot of fun coming back to Seattle."
He spent two seasons as the Orioles' closer, saving 51 games and earning an American League All-Star berth in 2008 before dealt to the Dodgers in July of '09. After a rough 2010 with Los Angeles, he signed with Atlanta and said he discovered an issue with his slide-step timing that was smoothed out as he returned to form last year.
The Mariners used Aaron Laffey as a left-hander in the bullpen for the first part of last season, but he was released in August. Cesar Jiminez, who posted a 5.40 ERA in eight appearances as a September callup, was the only left-handed reliever with Major League experience on the 40-man roster prior to Sherrill's signing.
Charlie Furbush could be a left-handed bullpen candidate, though he'll likely be given a shot at making the starting rotation. The club also has signed lefty relievers Sean Henn and Steve Garrison to Minor League deals with Major League camp invites. Rule 5 Draft pick Lucas Luetge is also a lefty specialist, though he never pitched above Double-A with the Brewers.
Zduriencik has filled two of his offseason priorities, with the signing of Sherrill as well as an earlier trade for catcher John Jaso from Tampa Bay.
Zduriencik would still like to add a veteran free-agent starting pitcher, with Jeff Francis and Kevin Millwood still on the market. He's mentioned the need for a backup shortstop or utility infielder, a role that could be filled by Japanese free agent Munenori Kawasaki, who has expressed interest in signing with Seattle.
And, of course, there's the issue of trying to add a bat, with Prince Fielder still on the market, along with a host of other less-talked-about free agents. Action figures to pick up on all those fronts after the holidays end on New Year's Day, though Zduriencik said he's been pushing hard to get deals done.
"I've been talking aggressively, but it takes two to tango," said Zduriencik. "People on the other end have to be willing, whether it's free agents or teams talking trade. You'd think [it'll pick up after the holidays], but who knows? You can only control what you can control. We'll just continue to do our job and have our conversations and see where it goes."