De Silva's legal expertise included war crimes, crimes against humanity, espionage, treason, drugs, terrorism, human rights, white-collar fraud and sports law. His clients included John Terry, Lee Bowyer, Buzz Aldrin, Harry Redknapp, Ron Atkinson, Hans Segers, Lawrence Dallaglio, Graham Rix and Jamie Osborne. De Silva was a member of the Governing Council of the Manorial Society. In October 2011, with the approval of Prime Minister David Cameron, de Silva was appointed to head a Review into collusion by the security services and other agencies of the state into the 1989 murder of the high-profile Belfast lawyer Pat Finucane. The report was published on 12 December 2012, and acknowledged "a willful and abject failure by successive Governments"; however, Finucane's family called the de Silva report a "sham." In 2019 the Supreme Court ruled that the official investigation into the Finucane murder was ineffective and failed to meet the required human rights standards.