In March 2006, Mitchell was granted leave to appeal against his conviction (and his length of sentence) at the High Court of Justiciary sitting as the Court of Criminal Appeal in Edinburgh, on the grounds of the trial judge's refusal to hear the original case outside of the city.
In November 2006, Mitchell won the right to appeal against his conviction for murder. Mitchell's legal team had wanted a number of grounds for appeal to be heard but the judges said only one would be allowed. Scotland's senior judge, the Lord Justice General, Lord Hamilton said they would allow a ground of appeal claiming that the trial judge erred in refusing to move Mitchell's case out of Edinburgh following publicity ahead of the proceedings. Lord Hamilton, who was sitting with Lord Kingarth and Lord MacLean, said: "We have come, with some hesitation, to the view that this ground is arguable." "There is an argument that the trial judge failed adequately to take into account the circumstances that the publicity might have had an impact of particular strength not only in the immediate locality of the crime but in a somewhat wider area embracing the city of Edinburgh and other towns in the Lothians," he said. There was a huge media fanfare surrounding the trial and this may have affected the final outcome. The fact that the jury were not put into a hotel for the night of the decision has also been cited as a factor. The Court of Criminal Appeal in Edinburgh heard Mitchell's appeal in February 2008, and in May 2008 his original conviction was upheld.
On 16 May 2008, the judges' verdict was given. Sitting over the appeal were Lord Osborne, Lord Kingarth and Lord Hamilton, who delivered the decision. They ruled that there was sufficient evidence in law that Mitchell could be convicted on and rejected his other grounds of appeal, yet stated that police questioning of Mitchell on 14 August 2003 had been "outrageous" and was "to be deplored."
Appeal against sentence refused
On 2 February 2011, Mitchell's appeal against sentence was refused by a two to one majority. Lord Justice Clerk, Lord Gill, sitting with Lord Hardie and Lady Cosgrove stated that he had the utmost sympathy for the family of the victim and that he understood entirely why this murder should have caused such public revulsion. Nevertheless, he was of the opinion that the sentencing judge should not have imposed a punishment part of such severity on such a young offender. He stated that justice would be done in this case if the punishment part of the sentence were fixed at 15 years. He did not consider that they were precluded from that disposal by anything said in the guidance given in HM Adv v Boyle and Ors (supra). He regretted, therefore, that he had to differ from his Lordship and her Ladyship.
Mitchell leaves court after the Cadder Appeal.
Cadder appeal refused
On 15 April 2011, Mitchell's bid to challenge his conviction for murder following a human rights ruling by the Supreme Court in the Cadder case was rejected. His lawyer told the Appeal Court in Edinburgh that his trial was unfair because he had no access to a lawyer during an interview. Lord Osborne sitting with Lord Hamilton (Lord Justice General) and Lord Kingarth told Mitchell that the application for leave to lodge the additional ground was refused. The appellant's appeal against sentence was finally disposed of on 2 February 2011 and in such circumstances there did not exist a live appeal in respect of which leave could be granted under section 110(4).