The British actor is expecting a baby with his girlfriend, make-up artist Naiyana Garth, who he has been dating since March (13).
A source tells Britain's Sunday Mirror the couple is "thrilled" about the baby news, adding, "Idris and Naiyana are so in love and this is the icing on the cake for them.
"They had been keeping it quiet as it's early in the pregnancy, but they've told family and friends and Naiyana is beginning to show. She is absolutely lovely and she's looking radiant. Her and Idris are a great couple and feel lucky to have found each other.
"He's a great dad and she'll be a brilliant mum. They can't wait for their new arrival."
Elba is already father to daughter Isan, 11, from a previous relationship.