The $250 "pre-party" tickets, which buys some one-on-one time with the couple, are sold out. A $50 ticket buys entry into the club, where Garner and Affleck will mingle.
Affleck recently agreed to help judge a contest sponsored by MoveOn.org to find the best ad supporting Obama's campaign.
The 35-year-old actor grew up in Cambridge, Mass., and filmed his directorial debut, the acclaimed movie "Gone, Baby, Gone," in Boston. He won an Academy Award in 1998 for writing the screenplay for "Good Will Hunting" with pal Matt Damon.
Garner, 35, has been filming scenes from a new movie in Boston. She is best known for her role as a secret agent in the TV series "Alias" and recently starred in "Juno."
The couple co-starred in the 2003 movie "Daredevil" and began dating the next year. They married in June 2005, and their daughter, Violet, was born later that year.