Collette, 37, has been married to musician Dave Galafassi since 2003 and they are the parents of a 2-year-old daughter.
"(We) are very happy to be expecting our second child together," the couple told People exclusively, adding Collette is due to give birth in the spring.
The child's gender was not reported.
Collette is best known for her work on TV's "The United States of Tara," and in the movies "The Hours," "About a Boy" and "Muriel's Wedding."
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