"'Alias' is not going to wind down as it comes to an end, it's going to rev up, and we're going to make it the event it deserves to be," ABC Entertainment President Stephen McPherson said in a statement.
Airing at 8 p.m. EST Thursday this season, "Alias" has struggled to hold its audience against the competition, especially CBS' "Survivor: Guatemala." Last week, the ABC show drew about 7 million viewers compared to about 19 million for "Survivor."
Garner and her husband, actor Ben Affleck, are expecting their first child around Christmas. Her pregnancy was written into "Alias" for her character, a globe-trotting spy.