[3][4] He was educated at King Edward's School, Birmingham, and read classics (literae humaniores) at Lincoln College, Oxford, graduating with an upper second-class honours in 2002.

[3] Whilst undertaking his postgraduate law studies in London from 2002 until 2004, he was the first intern at the recently established Policy Exchange, later becoming a Research Fellow, working on policing [6] and constitutional reform.

[12] He has acted in over 200 reported cases, including 18 Supreme Court appeals (making him one of the top ten currently practising barristers by number of appearances in the Supreme Court since its opening in 2009),[13] notable examples being R(Cart) v. Upper Tribunal [2012] 1 AC 663 concerning the constitutional principles relating to judicial review,[14] R(Al-Skeini) v. Secretary of State for Defence [2008] 1 AC 153 concerning the territorial scope of the Human Rights Act 1998, in which as a junior barrister he was led by Keir Starmer who was then a practising Queen’s Counsel,[15] as well as judicial reviews concerning HS2 (R (HS2 Action Alliance Ltd) v Secretary of State for Transport),[16] the proposed third runway at Heathrow Airport,[17] the expansion of Stansted Airport,[18] and a new stadium at Casement Park.

[29] In January 2025, he spoke out in defence of Attorney General Richard Hermer KC, who had been criticised in the conservative media for having previously represented clients such as Gerry Adams and Shamina Begum, citing the 'cab rank rule' of the independent bar in the UK as playing a critical role in ensuring equality before the law.

[30] Banner is a Patron of the Restart Foundation (a charity focused upon improving mental health in Ukraine),[31] a Trustee of Prism the Gift Fund (a facilitator for charitable giving),[32] and a supporter of Sir Brian May's animal-welfare and nature-conservation organisation Save Me.