Tennant, who took over the role from Christopher Eccleston in the 2005 Christmas special, has scooped an array of awards for his performances in the BBC show and won affection from the viewing public.
Before he departs, Tennant will appear in the BBC Christmas special this year, four specials in 2009, as well as a final special edition in which his character will regenerate into a new Doctor.
Bookies are already drawing up the odds on who will replace him, with Paddy Power reckoning Paterson Joseph, who has appeared in 'Peep Show' and 'Green Wing', as the favourite to take on the role. Joseph, who has already appeared in a number of episodes alongside Eccleston, playing Roderick, would be the first black Doctor.
'Life On Mars' star John Simm has been given odds of 8-1 to enter the Tardis, despite the fact that he has appeared in the programme as the Doctor's nemesis, The Master. Other names linked to the role include David Morrisey and James Nesbitt.
Tennant became the 10th actor to star as The Doctor since the programme made its TV debut back in 1963. Others who have made the role their own include John Pertwee, Peter Davidson and Tom Baker, who competes with Tennant in the hearts of the public for the accolade of most popular Doctor ever.
Tennant said: "I've had the most brilliant, bewildering and life-changing time working on Doctor Who. I have loved every day of it.
"It would be very easy to cling to the Tardis console forever and I fear that if I don't take a deep breath and make the decision to move on now, then I simply never will."
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