Comic James and charity worker Julia - who he calls Jules - are already parents to son Max, who was born in March 2011, and are now looking forward to welcoming another bundle of joy.
James' rep confirmed the couple's happy news to Reveal.
Gavin & Stacey star James was introduced to Jules through their mutual friend, actor Dominic Cooper, and they married in a lavish £250,000 ceremony at Babington House, Somerset, in September 2012.
James had proposed to Jules on Christmas day, three months before their baby son Max was born, and guests at their wedding included Jimmy Carr, David Walliams and former Radio 1 DJ Chris Moyles.
Snow Patrol star Gary Lightbody was also on hand to serenade the couple.
Celebrities who have announced pregnancies in 2014:
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