- His grandfather, Archie McLeod, was a professional soccer player with Derry City F.C. in Northern Ireland during the 1930s, and Tennant is a member of the club's supporters.
- His father, a retired minister, is a former Moderator of the General Assembly of the Church of Scotland.
- As a teenager in the 1980s, wanted to join the actors' union Equity, which already had a person registered with his birth name (David McDonald); he adopted the stage surname Tennant, after Neil Tennant of the Pet Shop Boys.
- Cut his acting teeth with Scotland's political 7:84 Theatre Group and had several starring roles with the Royal Shakespeare Company (Romeo and Juliet; As You Like It).
- In 2005, became the tenth incarnation of the mysterious time traveler in the sci-fi cult favorite Doctor Who, the show that made him want to be an actor (when Tom Baker was playing the role in the 1970s).
- In 2007, under his birth name, was added to the 159th edition of Who's Who, the United Kingdom's oldest biographical yearbook.
- Has provided voices for the audio-book versions of Cressida Cowell's How to Train Your Dragon series.
- Supports the Association for International Cancer Research and Headway Essex, a brain-injury charity.