The happy twosome welcomed a baby girl on Friday, reports Us Weekly.
Mendes went to great lengths to hide her pregnancy, avoiding the public eye as much as possible. Her last red carpet appearance was in March.
News broke in June that the star was already seven months along. People earlier reported she was due in October.
Ryan, 33, and Eva, 40, began dating in 2011 after starring in the dark indie “A Place Beyond the Pines,” and more recently collaborated on Gosling’s directorial debut, “Lost River,” which premiered at Cannes this year.