Turnbull worked initially in general practice at the Bar, but by 1988 had developed specialities in criminal defence and fraud. He was appointed an Advocate Depute in 1995, taking silk in 1996, and returning to private practice in 1997. In 1998, he was appointed one of two senior prosecuting counsel in the Lockerbie bombing trial, along with Alastair Campbell QC (now Lord Bracadale).[3] In February 2001, he was appointed Principal Advocate Depute, resigning to return to private practice in 2006. He was succeeded as Principal Advocate Depute by John Beckett QC, who would later serve as Solicitor General,[4] being appointed to the Bench later that year.[5][6]
During his time working as Advocate Depute, Alan Turnbull prosecuted Scotland's most difficult criminal cases including that of William Beggs, known as the "Limbs in the Loch" murder. Other notable cases included Luke Mitchell, who was convicted of murdering his girlfriend, Jodi Jones, in Dalkeith; and businessman Nat Fraser, who was convicted of killing his wife, Arlene Fraser, in January 2003.
On 12 June 2023, the Secretary of State for Northern Ireland Chris Heaton-Harris, announced that Lord Turnbull will chair the Omagh Bombing Inquiry due to Turnbull's "previous experience of working on terrorism cases".[10]
