In a dramatic opening sequence, the new Time Lord arrived on screen clinging to the open door of the Tardis as it hurtled across the London skyline.
Smith (27) is the 11th actor to take on the role of the time travelling Doctor and BBC chiefs will be hoping he becomes as popular as his predecessor, David Tennant.
Tennant's first appearance as the Doctor in April 2006 also attracted eight million viewers.
Audience figures for the show last night peaked at 8.4m and averaged 8m, an audience share of 36.9%, the BBC said.
A poll for the Digital Spy website saw 67% rate the show as “very good”.
Meanwhile, on ITV Harry Hill's TV Burp was watched by an average of just 3.5m viewers.
BBC1 has enjoyed a good weekend in terms of its audience share, with new Andrew Lloyd Webber show Over The Rainbow attracting 5.5m viewers.
The channel also featured the Thames Boat Race and Malaysian Grand Prix.