Born in North London, England, to choreographer Nigel Lythgoe and dancer Bonita Lythgoe, he grew up in Cuffley, Hertfordshire. After attending Keble Preparatory School in Winchmore Hill, North London, he later attended Felsted boarding school in Essex.  After completing 10 GCSEs he attended Oaklands college in St.Albans for his A-Levels.
Upon completion of his studies worked for London Weekend Television as a senior runner and an Assistant Floor Manager. His credits include the Late Show with David Letterman, The Royal Variety Performance, Don't Forget Your Toothbrush, An Audience with ...., Gladiators, The Brian Conley Show, The Big Big Talent Show, British Comedy Awards.
In 1993 Lythgoe traveled to Australia to work on the Aussie version of Gladiators for Kevin Jacobson Productions. The monthlong engagement turned into a yearlong commitment, when Lythgoe decided to stay in Sydney working for the Seven Network. His titles ranged from 3rd Assistant Director to Floor Manager, and later a Researcher and then Associate Producer.
After a year Lythgoe returned to London, England. He worked as the 1st Assistant Director for Sky's drama series Dream Team, produced by Hewland International. During this time he also attended the National Film and Television School.
After completing the first series, Lythgoe emigrated permanently to Sydney, Australia. Returning to the Seven Network he worked on the Sydney 2000 Olympics, Roy & HG's Money, The Monday Dump, Saturday Disney, House of Hits, The Morning Shift, Big Arvo, People's Choice Awards, along with numerous sports events including the Bledisloe Cup, AFL, Super 12 Rugby, the Lions Tour.
In 1999 Lythgoe was employed by Screentime Pty. Ltd. working in Program Development. After completing one of Australia's highest rating and groundbreaking series, Popstars Season 2 and 3, Lythgoe coerced his father, Nigel Lythgoe, to license the format for Britain's ITV network. With the overwhelming success of Popstars in the UK, Nigel formed 19 Television with Simon Fuller, and the format morphed into Pop Idol. This format was later sold to the USA, known as American Idol.
In 2002 Lythgoe left Australia and moved to Hollywood to help produce American Idol with his father, Nigel. Lythgoe produced some of Idol's biggest success stories including Carrie Underwood and Ruben Studard. During this period Lythgoe was also the coordinating producer for So You Think You Can Dance. After six seasons of Idol and two of SYTYCD Lythgoe was poached by Steven Spielberg and Mark Burnett as a producer for the Fox Network's On The Lot. Upon completion Lythgoe was employed as an Executive for American Idol's parent company, Fremantle Media North America. During his contract Lythgoe produced CMT's Can You Duet, NBC's Celebrity Family Feud, Fox's Osbourne Reloaded and advised on America's Got Talent, I've Got Your Number and Let's Make A Deal.
In 2010 Lythgoe left Fremantle Media and setup his own company, Legacy Productions. The production company established development deals with a number of development Executive Producers in Hollywood. In the first quarter of 2011, Legacy Productions, with Simon as the Showrunner, produced "CMTs Next Superstar" for CMT Network. The series was commissioned for a second season, but was later cancelled for creative and budgetary reasons. In 2012 Simon developed, directed and was the Showrunner on "A Chance to Dance" for Ovation and "Opening Act" for E! Network.
Lythgoe was married to Fiona Lazaredes on 3 January 1999. They have three children, Kyan David Anthony Lythgoe, Tighe Jamie George Lythgoe and Dominie Antonia Lythgoe. The couple divorced in 2004. In 2008 Lythgoe married to Tifanie A. White, a makeup artist on American Idol and So You Think You Can Dance. The couple divorced in 2012. There has been speculation that Simon Lythgoe is engaged to CMT host and Extra correspondent Alecia Davis.