The couple - who met on the set of `Step Up` in 2006 and married in 2009 - will welcome the new addition to their family next year.
Channing`s representative told People magazine: "JennaDewan-Tatum and Channing Tatum are pleased to announce that they are expecting the birth of their first child next year."
While Jenna and Channing, both 32, have spoken previously about wanting to start a family, the pregnancy was reportedly a "total surprise", according to Us Weekly.
The `Magic Mike` actor recently revealed he wants a large family, but admitted Jenna may not agree. He said: "I`m ready; I think she`s ready. The first number that pops into my head is three, but I just want one to be healthy and then we`ll see where we go after that."
"It`s really easy for us guys to say, `I want like 15 kids`, Jenna will be like, `Well you better get another wife!`"
Despite the couple`s busy work schedules, they make sure to spend time with each other by having a rule by where they never spend too much time apart.
Jenna said: "We do everything other happy couples do ... You communicate, you make sure you see each other.
"Our schedules make it a little difficult at times and you have to make sure you have, like a rule. We have a like a two-week rule. So we see each other every two weeks. If you want to make it work, you make it work. That`s what happens."