While her first name is Kate, she chose to go by KT as her first name, saying "[Kate] just makes me think of a buxom lass baking bread for her man working in the fields. I have no problem with that, but it's just not really how I pictured being a rock star." Also, Tunstall spells her first name KT (as opposed to Katie) to differentiate herself from fellow singer Katie Melua.

Tunstall sparked some controversy in 2005 when she publicly bashed singer/songwriter Dido, stating that the artist "can't fucking sing" after several fans compared the two musically. Tunstall later apologized, stating that she did not want to be involved in a public feud.

Tunstall denies rumours or assumptions that she is a lesbian by expressing gratitude to her gay and lesbian following, and says the rainbow patterned braces on her debut record cover were not intended as a statement of identity or politics as she was unaware of the symbolism at the time.

Since 2003, Tunstall has been dating