The Hollywood couple is engaged to be married and already expecting a baby, report news sources. It will be the first marriage for both actors, who have been dating for four years.
Although they've both appeared in high-profile studio films, they've made the biggest splashes in indie movies. Gyllenhaal, 28, is the older sister of "Brokeback Mountain" star Jake Gyllenhaal. They co-starred in the cult favorite "Donnie Darko," but she really made a name for herself as the titular submissive in 2002's "Secretary" opposite James Spader.
Her other credits include "Adaptation," "Mona Lisa Smile," the upcoming "Trust the Man" and Oliver Stone's "World Trade Center."
Sarsgaard, 35, may be more familiar to mainstream audiences. His recent studio films include "Jarhead," "Flightplan" and "The Skeleton Key." His other film credits include critically acclaimed roles in "Boys Don't Cry," "Shattered Glass," "Garden State" and "Kinsey."