Mitchell competed in his first junior ITF under 18 event in December 2005 as a 13 year old, he was beaten soundly in the first round by James Wong 6-3 6-1. Mitchell had varying success between Australian and New Zealand tournaments through 2006-2008 which included his first final in Darwin. Mitchell stopped playing junior tournaments in 2009 to focus on senior tournaments and in doing so entered his last season as a junior in 2010 without a ranking. Tennis Australia provided wildcards into the Traralgon International and the Australian Open junior event and Mitchell did not disappoint. He reached the final of the Traralgon International and the quarterfinals of the Australian Open juniors event. Following his successful Australian summer Mitchell won his first and only junior title in Nonthaburi, Thailand where he defeated Suk-Young Jeong in the final 7-5 6-3.
In June, Mitchell participated in a futures tournament in Australia, where he lost in straight sets in the first round to Krishananth Balakrishnan of Australia. In November 2010, Mitchell entered the Australian Open Wild Card Play-offs, hoping to win himself a main draw wild card for the 2011 Australian Open. However, Mitchell lost to fellow Australian and fourth seed, Matthew Ebden in the quarterfinals.
Won tournament; or reached Final; Semifinal; Quarter-final; Round 4, 3, 2, 1; competed at a Round Robin stage; lost in Qualification Round; absent from tournament event; played in a Davis Cup Zonal Group (with its number indication) or Play-off; won a bronze, silver (F or S) or gold medal at the Olympics; a downgraded Masters Series/1000 tournament (Not a Masters Series); or a tournament that was Not Held in a given year.
To avoid confusion and double counting, these charts are updated either at the conclusion of a tournament, or when the player's participation in the tournament has ended.