Vernon's debut at an international athletics competition was at the 2004 IAAF World Cross Country Championships where he competed in the 8,000-metre junior men's race; finishing 64th in a time of 27 minutes and 12 seconds.

[3] Vernon's next international competition was the 2005 IAAF World Cross Country Championships where he again competed in the junior men's race, this time finishing 48th.

[2] In December 2005 he won his first international medal in the European Junior Cross Country Championships finishing 2nd behind Hungary's Barnabás Bene.

[2] At the 2007 European Athletics U23 Championships Vernon competed in the 5000 metres and finished seventh in a time of 13 minutes and 59.24 seconds.

[2] Also in 2008 was the 2008 IAAF World Cross Country Championships where Vernon finished 115th in the 12 kilometres senior men's race.

[2] At the 2009 European Cross Country Championships in Dublin Vernon competed in the men's senior race; finishing 12th.

[2] In March 2011 Vernon competed in the senior men's race at the 2011 IAAF World Cross Country Championships and finished 58th.

[2] Vernon's next major competition was the 2011 European Cross Country Championships where he finished ninth in the senior men's race.

[8] In February 2015 Vernon was involved in an argument with fellow British athlete Mo Farah on Twitter.