He first appeared on 7 March 2001, aged just fifteen, and quickly rattled off eight high-scoring wins to become an octochamp, the only one of the series. He was the clear #1 seed for the finals, but was unexpectedly defeated in the quarter-final 45 – 50 by John Rainsden.
McMahon returned two years later for Championship of Champions XI, being invited back after Series 46 semi-finalist Paul Ryan was unable to make the studio dates, but lost 99 – 97 to John Rawnsley in the first round.
McMahon is now an Apterite. He is also a competitive Scrabble player and won the prestigious ABSP-organised British Matchplay Championship in 2012, beating fellow Countdown alumnus Paul Gallen in the deciding game. He was also a semi-finalist at the 2018 Mattel World Scrabble Championships in Torquay.
|#||Date||Type||Contestant 1||Score||Contestant 2||Guest||Lex||Max|
|2963||7/03/2001||P||Heather Jenkins||44 – 57||Kevin McMahon||Victor Ubogu||Richard Samson||74|
|2964||8/03/2001||P||Kevin McMahon||56 – 28||Betty Whitear||Victor Ubogu||Richard Samson||74|
|2965||9/03/2001||P||Kevin McMahon||52 – 29||Brian Howard||Victor Ubogu||Richard Samson||74|
|2966||12/03/2001||P||Kevin McMahon||70* – 60||Gareth Fuller||Gloria Hunniford||Richard Samson||86|
|2967||13/03/2001||P||Kevin McMahon||63 – 25||John Frankel||Gloria Hunniford||Richard Samson||75|
|2968||14/03/2001||P||Kevin McMahon||68 – 13||Linda Clark||Gloria Hunniford||Richard Samson||73|
|2969||15/03/2001||P||Kevin McMahon||74 – 52||Mark Sperinck||Gloria Hunniford||Richard Samson||84|
|2970||16/03/2001||P||Kevin McMahon||68 – 23||Julie Devine||Gloria Hunniford||Richard Samson||73|
|3036||21/06/2001||QF||Kevin McMahon||45 – 50||John Rainsden||Martin Jarvis||Damian Eadie||72|
|3393||9/01/2003||CP||John Rawnsley||99 – 97||Kevin McMahon||Martin Jarvis||Susie Dent||141|