The Giants acquired Guillen on Friday and also received cash considerations from the Kansas City Royals in exchange for a player to be named.
"We didn't acquire him to be on the bench," said manager Bruce Bochy, who plans to use Guillen somewhere in the middle of the batting order.
The Giants haven't been to the playoffs since 2003 and were in the NL wild-card chase until mid-September last season. Getting over the hump in 2010 and ending the six-year drought is the franchise's top priority.
San Francisco general manager Brian Sabean has been busy upgrading his roster in recent weeks.
"Anybody who knows Sabes knows he wants to win and will do what it takes to get us where we need to get," second baseman Freddy Sanchez said. "Winning the division is the No. 1 goal and getting to the playoffs. He keeps going out and putting pieces together."
The Royals announced the deal hours before the Giants hosted the first-place San Diego Padres in an NL West showdown at AT&T Park. San Diego held a 2½-game division lead heading into the weekend series. The Giants, who will be Guillen's 10th major league team in 14 seasons, said the slugger was set to get into town late Friday and would miss the series opener.
Guillen is expected to be in uniform Saturday, when the club will be forced to make a corresponding roster move.
The Royals designated Guillen for assignment last Thursday, giving them 10 days to trade him, release him or send him to the minors if he cleared waivers.
Sabean has acknowledged he believes the Giants are a playoff team but that keeping pace with the Padres will be tough.
Guillen has had his share of issues along the way, but San Francisco seems unconcerned about his reputation of disrupting clubhouses.
"We're convinced he's ready to play baseball, coming to a winning situation, which Kansas City wasn't," Sabean said. "We've got a great clubhouse. The players run our clubhouse. I don't see any kind of problem."
Guillen was suspended by the Los Angeles Angels for the last two weeks of the 2004 regular season and postseason for inappropriate conduct after expressing his displeasure with manager Mike Scioscia. After the year, Guillen was traded to the Washington Nationals.
In July 2008, Guillen got into a heated clubhouse exchange with Royals pitching coach Bob McClure, knocking over chairs before several players separated them before a game at Tampa Bay. Guillen also unleashed a profanity-filled tirade against his teammates that May.
Bochy spoke with several of Guillen's former managers or coaches and received good reports. Bochy also talked to Guillen himself.
"He's healthy. He takes care of himself," Bochy said. "I heard enough and talking to him that he'll be a good fit here."
Sabean found the left-handed reliever the Giants needed when he acquired Javier Lopez from the Pittsburgh Pirates at the July 31 trade deadline. San Francisco also acquired righty reliever Ramon Ramirez from the Boston Red Sox at the deadline. That's after the Giants got resurgent slugger Pat Burrell in June following his poor start with Tampa Bay. Burrell is thrilled with the fresh start and has jump-started the offense of late.
The 34-year-old Guillen signed a $36 million, three-year contract three years ago that made him the Royals' highest-paid player per year in team history. He spent the 2003 season in the Bay Area with the Oakland Athletics.
Just a month ago, Guillen put together a hitting streak that stretched to more than 20 games. He was batting .255 with a team-best 16 homers and 62 RBIs when he was cut by the Royals. The move allowed Kansas City to play highly touted prospect Kila Ka'aihue every day, and Guillen also didn't like being a reserve.
The Royals will miss Guillen in spite of his mood swings.
"He's been in this family for the most part of three years," manager Ned Yost said before the Royals hosted the Yankees. "There were times when Jose would get upset with individuals and individuals would get upset with Jose, but at the end of the day everybody was here to win baseball games. And that was his major goal, to come out and have himself prepared and be ready to help this team win a baseball game.
"There wasn't a day that I've been here that wasn't the case. ... He set a good example in terms of how to respect the game, how to try to play the game right and play the game hard," he said.
Guillen struggled with injuries in Kansas City. He played in only 81 games last year and hit nine homers, tied for his fewest since 2002. He was out for weeks after injuring his knee while he was putting on a shin guard and missed several days of spring training in 2009 after deciding to rip out an ingrown toenail with a pair of pliers.
All Sanchez cares about is Guillen can help the team over the final six weeks -- any of Guillen's problems are now in the past.
"He's a talented player who can come in and help in so many ways," Sanchez said. "We have a fun clubhouse. At the end of the day everybody wants to win."