The 27-year-old, who is the daughter of Aerosmith frontman Steve Tyler and model Bebe Buell, gave birth in New York on Tuesday.
"They are both doing great", said the actress's publicist Stephen Huvane, who added the child has yet to be named.
Tyler, who starred in the Lord of the Rings films, is married to Royston Langdon from the band Spacehog. The pair tied the knot in March 2003.
The actress played the elf Arwen in all three episodes of The Lord of the Rings trilogy.
Her performance - along with the ensemble cast of the film's third and final outing - won a series of awards earlier this year.
She has also appeared in films such as Armageddon, Inventing the Abbotts and That Thing You Do.