The Eagles needed a backup quarterback in case McNabb, who suffered a broken rib in Philadelphia's 38-10 win over Carolina in the season opener, is not able to play this week against the New Orleans Saints.
Third-year pro Kevin Kolb filled in for McNabb and will start if McNabb is out, coach Andy Reid said.
"Whether it's a week or two weeks or the entire season, I'm excited about the opportunity," Garcia said in a conference call. "As far as a team I can go to and blend right in, this is the team for me to do that."
Garcia, who was signed by Oakland in the offseason to push JaMarcus Russell and serve as a mentor to the former No. 1 overall draft pick, was released by the Raiders on Sept. 5 after playing little in the preseason. He said he could've stayed with Oakland, but didn't think it was the right fit. But he also wasn't ready to call it a career.
"I didn't want it to be over," Garcia said. "I feel there's a lot of quality football left in me."
A four-time Pro Bowl selection, Garcia played well in his previous stint with the Eagles three seasons ago, throwing 11 touchdown passes against two interceptions in eight starts. In the process, he also became very popular with fans.
"I know the circumstances are different," Garcia said. "I'm OK with whatever helps the team."
Philadelphia's other quarterback, Michael Vick, is not eligible this week because he was suspended for the first two regular-season games as the last part of the NFL's penalty for his role in a dogfighting ring.
"We're lucky Jeff was available," Reid said on his weekly radio show. "He's someone who knows this offense and has been very successful in this offense. He can be a positive influence on Kevin Kolb."
The 39-year-old Garcia began his career with San Francisco in 1999. He replaced Hall of Fame QB Steve Young, put up big passing numbers with Terrell Owens as his main target and led the 49ers to two playoff appearances in his first three seasons as a full-time starter.
Garcia's career took a downward turn after he left the rebuilding 49ers in 2004. He spent forgettable seasons with Cleveland and Detroit before rejuvenating his career in Philadelphia in '06.
Garcia stepped in when McNabb tore his ACL, led the Eagles to a 5-1 record, an NFC East title and a playoff win over the New York Giants. His final game with Philadelphia was a loss at New Orleans in the divisional playoffs.
In his brief time with the Eagles, Garcia completely won over the tough Philly fans with his fiery personality and win-at-all-costs attitude.
A company made up T-shirts featuring Garcia with his fists up in a boxer's stance above the caption: "A Fighter Fights."
The Eagles didn't re-sign Garcia after that season and he went to Tampa Bay. Garcia led the Buccaneers to the NFC South title in 2007 and earned a trip to Hawaii.
Garcia has thrown for 25,537 yards, 161 touchdowns and 83 interceptions in 124 career games. He's completed 61.6 percent of his passes and has a QB rating of 87.5. Garcia is 58-58 as a starter.
McNabb, Vick and Garcia have been to a combined 12 Pro Bowls.