Lloyd was born in Dover and educated at West Hill Park School in Titchfield, Hants; The King's School, Canterbury; and Trinity College, Cambridge. There he befriended, and later shared a flat with Douglas Adams. He worked as a radio producer at the BBC 1974–1978 and created The News Quiz, The News Huddlines, To The Manor Born (with Peter Spence) and Quote... Unquote (with Nigel Rees). He wrote Hordes of the Things (as J. H. W. Lloyd) with Andrew Marshall, co-authored two episodes of Doctor Snuggles with Douglas Adams and then went on to co-write the fifth and sixth episodes of the first radio series of The Hitchhiker's Guide to the Galaxy with him. (Douglas Adams wrote all the other previous and subsequent episodes solo, as well as the television adaptation — though Lloyd was involved in the TV series as Associate Producer.) Lloyd then worked as a TV producer at both the BBC and ITV 1979–1989 where he created Not the Nine O'Clock News (with Sean Hardie) and Spitting Image (with Peter Fluck and Roger Law). He also produced all four Blackadder series.

Lloyd has worked as a TV commercials director on and off since 1987. He is married with three children and lives in the UK. His first new TV series for 14 years, QI (short for Quite Interesting, and a deliberate reversal of IQ), starring Stephen Fry and Alan Davies, began on 11 September 2003 at 10pm on BBC2 for a run of 12 episodes. It is now in its eighth series, which started on BBC One in September 2010, produced by Piers Fletcher. All the episodes of QI (including the pilot) have been directed by Ian Lorimer. Lloyd currently presents the radio series, The Museum of Curiosity (2008), which he co-created with producers Richard Turner & Dan Schreiber and former co-host Bill Bailey.

He co-authored the books:

• Not! The Nine O'Clock News
• Not 1982
• Not 1983
• Not the Royal Wedding
• Not the General Election
• The Meaning of Liff (1983, with Douglas Adams)
• The Deeper Meaning of Liff (1990, with Douglas Adams)
• The Appallingly Disrespectful Spitting Image Book
• Spitting Image
• The Whole Damn Dynasty 1485—1917 (2000, with Richard Curtis and Rowan Atkinson)
• The Book of General Ignorance (2006, with John Mitchinson and the QI Elves)
• The Book of Animal Ignorance (2007, with John Mitchinson and the QI Elves)
• Advanced Banter (2008, with John Mitchinson and the QI Elves)
• The QI Book of the Dead (2009, with John Mitchinson and the QI Elves)
• The QI Annual E [editor] (2007, with various authors)
• The QI Annual F [co-editor] (2008, with John Mitchinson [co-editor] and various authors)
• The QI Annual G [editor] (2009, with various authors)