Smith is the 11th actor to play the iconic time traveler in the long-running science-fiction series. At 27, he is also the youngest actor to play the part.
His first episode aired Saturday night. Its viewership peaked at 8.4 million and averaged 8 million, the BBC said Monday.
Scottish actor David Tennant, who had played the Doctor since 2006, left the show in January.
2014: The Year in Music [PHOTOS]