Cantley served in the British Army in the Second World War, first in the Royal Artillery and then on staff appointments, spending time in North Africa and Italy.
One of his last trials was leading for the prosecution when Gwynne Evans and Peter Allen were convicted for the murder of John Alan West in 1964, which led to the last two judicial executions in Britain before the abolition of the death penalty in 1965.
He had a low public profile until he presided at the trial of Jeremy Thorpe in May–June 1979, shortly after the 1979 UK general election on 3 May 1979 - so much so that no press agency could find a photograph of him.
At the 1979 Secret Policeman's Ball, in aid of Amnesty International, the biased summing up speech by Mr Justice Cantley was parodied by Peter Cook.
[3] Notwithstanding marked and widespread public disquiet at the biased summing-up in the Thorpe trial, Cantley was considered as Presiding Judge on the South Eastern Circuit, but declined in order to become Treasurer of Middle Temple in 1981.