Dent is well known as the resident lexicographer and adjudicator on Channel 4's long-running game show Countdown. She is the longest-serving member of the show's current on-screen team, having first appeared in 1992; she has made over 2500 appearances. Alison Heard replaced Dent as lexicographer over the winter of 2007–08 while she was on maternity leave. She also works on the spin-off show, 8 Out of 10 Cats Does Countdown.
From 2003 to 2007, Dent was the author of a series of annual Language Reports for the Oxford University Press (OUP). The first was entitled simply The Language Report, followed by Larpers and Shroomers (2004), Fanboys and Overdogs (2005), The Like, Language Report for Real (2006) and The Language Report: English on the Move 2000 – 2007 (2007). The format of this publication was revised for 2008 as an A–Z collection of new and newly resurrected words. It was published in October 2008 as Words of the Year. In 2005 the same publisher issued Winning Ways (ISBN 0199198748). 2009 OUP published her latest work: What Made the Crocodile Cry? 101 questions about the English language (ISBN 0199574154). Dent's book about dialects, How to Talk Like a Local (ISBN 1905211791), was published in March 2010.