As lead runner of the relay team for 26th May 2012, the actor will carry the Olympic Flame through part of Cardiff close to the BBC Roath Lock Studios where Doctor Who is produced.
Smith commented: "To carry the Torch is an honour, one I thought I'd never get. I'm very excited!"
The run will begin at around 6.20am at the Norwegian Church Arts Centre, Harbour Drive, Cardiff Bay, CF10 4PA. Smith will then hand over the Olympic Flame at the Senedd, National Assembly Building, Cardiff, CF99 1NA.
Live coverage of the run will be broadcast via the official BBC Olympics website.
The Doctor Who website team will also be in Cardiff to provide coverage of the event.
(Source: BBC Doctor Who)