The audience peaked at 9.8m viewers and a 47% share of the audience, with an average audience of 9.4m tuning in between 6.40pm-7.45pm on BBC One.
Secrecy had shrouded the episode amid speculation he would not survive an attack by his arch enemies, the Daleks.
But the Doctor recovered leaving the way open for Tennant to return for a fifth series in 2010.
The previous week's episode had ended on a cliff-hanger when the Doctor was shot by a Dalek and apparently began to regenerate.
However, with the help of his companions, past and present, the Doctor once again beat the Daleks and their evil creator, Davros. When he does return, latest companion Catherine Tate will not. She was left behind on Earth at the end of the episode with her memories of the Doctor gone.
Tennant has been confirmed to star in the lead role for a number of BBC One 'Doctor Who' specials next year and will return in a Christmas episode, which will see the return of the Cybermen.
The fifth series will be penned by Bafta-winning writer Steven Moffat, who is to take over from current writer and executive producer, Russell T Davies.
Earlier in the day, 14-year-old British tennis sensation Laura Robson proved a bigger draw for BBC viewers than the top women's players.
Robson's victory in the Wimbledon girls' title was watched by 4.5m viewers, a million more than saw Venus Williams beat her sister Serena in the women's final.
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