He broke the news on Twitter, telling more than 1million followers about the new addition to the family.
"My Son Winston Elba was born yesterday..Truly Amazing :-)," he captioned a shot of the infant gripping to his index finger.
My Son Winston Elba was born yesterday..Truly Amazing :-) pic.twitter.com/MrSEQPZo4z— Idris Elba (@idriselba) April 18, 2014
The star of Mandela: Long Walk to Freedom began dating Nayiana in March 2013 and the couple were said to be "thrilled" when she fell pregnant.
Idris also has an 11-year-old daughter, Isan, from a previous relationship. The dashing actor has certainly been full of high spirits lately - he was seen beaming while photobombing Oprah Winfrey at the NAACP Awards.
Then the 41-year-old actor was at the centre of an internet phenomenon when a man tweeted a poem complaining about his wife's obession with Idris.
Idris Elba and his girlfriend have welcomed a child
Entitled I Am Sorry I'm Not Idris Elba, it included the lines: "I am just a regular man / With a regular 9-5 / That does regular things / But you let the characters he plays / And the pictures he takes / Interfere with our relationship /I'm building companionship / But he's your man crush / When it's me you should be crushing on."
Idris seemed to enjoy the joke a supercool image of himself with the caption: "I am NOT sorry I'm Idris Elba.
This happy phase in his life is probably down to his new love.
The actor was "truly amazed" by the birth of his child
A source told The Sun: "They've been together for a few months but it's really ramped up recently. They get on brilliantly and she's a real hit with his family and friends.
"Idris is known as a ladies' man but he's really not at all. He'd rather have banter at the bar than spend all night (hitting) on women. Although he doesn't have to try anyway, women flock to him."
The dashing Londoner has become a huge star especially in the States thanks to roles in TV series The Wire and movie American Gangster. He also moonlights as a DJ under the moniker Big Driis. In 2013 he was ranked second on People's Sexiest Man Alive list.