The 27-year-old Swiss star confirmed the news on his blog.
"Mirka and I are excited to let you know that we will be parents this summer!" People quoted Federer as writing on his blog.
"Mirka is pregnant and we are so happy to be starting a family together. This is a dream come true for us.
"We love children and we are looking forward to being parents for the first time. Mirka is feeling great and everything is going well," he added.
Grand Slam champ Federer and former Women's Tennis Association (WTA) player Mirka have been together since the 2000 Sydney Olympics, where they met while representing Switzerland.