Smith who will become the eleventh, and youngest, incarnation of the Time Lord was unveiled during a special episode of Doctor Who Confidential on BBC One.
Steven Moffat, the producer of the forthcoming fifth series of the sci-fi hit said Smith was perfect casting because he was someone who was old and young at the same time.
The announcement, which was heavily trailed by the BBC in the run up to the broadcast, ends months of speculation sparked by Tennant’s announcement in October that he will step down as the Doctor.
Of his casting, Smith said: “I’m flabbergasted. I haven’t slept really! [Doctor Who] is an iconic part of our culture, and now I’m taking that on. It’s nerve wracking. Exciting. Exciting.
“It’s an iconic part of our culture, my grandad knows about it, my dad knows about it, it’s been going since 1963 it has the iconic status of Robin Hood or Sherlock Holmes.”
Tennant, who took over from Christopher Eccleston in 2005, will now complete four hour long specials.
In the final episode he will undergo the famous regeneration scene that will see Tennant transform into Smith.
Some of the country’s most famous actors including David Morrissey, who played a character called the Doctor in last year’s Christmas Day Special The Next Doctor, Chiwitel Ejiofor, Patterson Joseph, James Nesbitt, Sean Pertwee, whose father Jon played the role in the 1970s, James McAvoy and John Simm who played the Master in the series, had all been tipped to play the role.
There was even speculation that the part could go to a woman and names including Catherine Zeta Jones, the Oscar winning star of Chicago, Jennifer Saunders, Meera Syal and Billie Piper, who starred as the Doctor’s former assistant Rose Tyler were all in the frame.
The new Doctor follows in the footsteps of William Hartnell, Patrick Troughton, Jon Pertwee, Tom Baker, Peter Davison, Colin Baker, Sylvester McCoy, Paul McGann, Christopher Eccleston and David Tennant.
Doctor Who, which was famously scrapped by the BBC in the 1980s, is now one of the Corporation’s most important programmes following its return to screens in 2005.
All four series have been huge ratings winners for the BBC and the four Christmas specials have been among the most successful programmes of recent years.
The most recent offering, The Next Doctor, was the third most watched programme on Christmas Day.
The success of the series has been largely down to the dramatist Russell T Davies, who has been the show’s leader writer and producer.
He recently revealed that leading figures within the BBC were so sceptical that the revamped show would be a success that they even considered casting Paul Daniels in the lead role.
Last year he suggested that Russell Tovey the Gavin and Stacey star who had appeared in the 2007 Christmas Day edition of the programme should take over from Tennant.
The quality of Davies’ writing has encouraged some of the biggest names in British entertainment to take part in the show including Kylie Minogue, Felicity Kendall, Sir Derek Jacobi, Maureen Lipman and Penelope Wilton.
Davies has announced he is stepping down from the franchise after completing the four specials.
His fellow writer and producer Steven Moffat will now assume overall responsibility for the programme.
Steven Moffat, who takes over from Russell T Davies as executive producer following the specials, said: “The Doctor is a very special part, and it takes a very special actor to play him. You need to be old and young at the same time, a boffin and an action hero, a cheeky schoolboy and the wise old man of the universe.
“As soon as Matt walked through the door, and blew us away with a bold and brand new take on the Time Lord, we knew we had our man.
“2010 is a long time away but rest assured the 11th Doctor is coming — and the universe has never been so safe.