The former South African president reached the milestone while in hospital in Pretoria, South Africa, where he has been receiving treatment for a recurring respiratory infection.
Mandela supporters gathered outside his hospital with balloons and flowers, while a host of famous friends also marked the occasion by posting celebratory messages on their Twitter.com pages.
Using the ailing leader's nickname Madiba, Whitaker writes, "My thoughts go to Nelson Mandela on this special day. Thank u (you) for being a source of inspiration and courage. Happy Bday (birthday) Madiba! Much love!"
Supermodel Campbell shared a photo of herself with Mandela, adding, "Happy birthday Madiba... I love you always and forever," and director Spike Lee posted, "Happy 95th Born Day To Nelson Mandela."
Singer Josh Groban and actress Melissa Joan Hart have also offered up birthday messages.