Krasinski, announced the news himself on twitter, noting that the couple have decided to name their baby girl Hazel, reported Contactmusic.
"Wanted to let the news out directly. Emily and I are so incredibly happy to welcome our daughter Hazel into the world today! Happy bday!," the actor posted.
The pair first met five years ago in 2008 and become engaged in August of the following year. They eventually tied the knot on July 10, 2010 in Como, Italy.
The 'Devil Wears Prada' actress first announced she is expecting her first child in September last year.