The married stars, who are expecting their first child together next year (14), will team up for animated movie The Wind Rises.
The historical fantasy film was a hit when it was released in Japan earlier this year (13), and now director/writer Miyazaki is bringing the movie to English-speaking audiences.
Krasinski will voice lead character Jiro Horikoshi, who designed Japan's World War Ii fighter planes, with Blunt as his love interest.
Other celebrities adding their voices to the film are Elijah Wood and Stanley Tucci, who is married to Blunt's sister, Felicity.
Miyazaki announced The Wind Rises would be his last movie shortly after its original release over the summer (13).