The 33-year-old first baseman officially rejoined the team he helped advance to the postseason in 2008 and 2010 after passing a physical Tuesday. He agreed to a $7.25 million, one-year deal last week after spending 2011 with the Chicago Cubs.
"I have so many great memories here. I look forward to creating even better ones," Pena said during a news conference at Tropicana Field. "I'm very optimistic about what the future holds for me, but most importantly for the ballclub."
Pena played for the Rays for four seasons from 2007-10, averaging 36 home runs, 102 RBIs and 93 walks. He was the AL comeback player of the year in 2007 and an All-Star in 2009
One of Tampa Bay's top offseason priorities was adding power to a lineup that was eighth in the AL in runs scored last year. Pena is the team's career home runs leader.
"I'm very excited about the team we have," said Pena, who left Tampa Bay as a free agent last winter, when the budget-conscious Rays slashed the payroll dramatically. "We have all the necessary tools and pieces in place to really make an impact."
Despite losing several key players, including Pena, Carl Crawford, pitcher Matt Garza and virtually the entire bullpen, Tampa Bay overcame a nine-game deficit in the wild-card standings in September to make the playoffs for the third time in four years.
Pena's return comes less than two weeks after the Rays stretched their already thin budget by acquiring another left-handed bat -- free agent Luke Scott, who figures to be the team's primary designated hitter. The former Baltimore Oriole received a $6 million, one-year deal.
"I don't think anyone in our front office would have thought that we would committed 13 or 14 million to the combination of designated hitter and first baseman," team president Matt Silverman said.
"We extended ourselves in part because of who Carlos is as a clubhouse presence, as a leader, as a fan favorite, but really about his play on the field. He adds a dimension of power to our lineup that we were missing last year," he said, "and we don't take a step back on defense."
Pena, who tied Mark Teixeira for the AL home run title with 39 three years ago, won a Gold Glove at first base in 2008.
Pena had 144 homers and drove in 407 runs during his first stint with the Rays, then batted .225 with 28 homers and 82 RBIs while earning $10 million in Chicago last year.
Silverman said Pena is an ideal fit for the Rays, though not necessarily the final piece the club hopes to put into place to try to challenge for their fourth playoff berth in five years. The club still could be open to a possible trade.
"We're not going win the headline battle in the offseason, especially in the AL East," Silverman said. "But if we can go into the season with the expectations of a winning season, with a team that can compete with the Red Sox, Yankees, Blue Jays and Orioles, we're going to do that. ... We have a lot of hope, a lot of optimism."