[2][9] Livingstone joined Lothian and Borders Police in 1992, rising swiftly through the ranks and eventually becoming head of that force's CID branch[4] and Assistant Chief Constable for Crime.

[9] He graduated with a master's degree from the John Jay College of Criminal Justice at the City University of New York, where he studied from 1998 as a Fulbright scholar;[2][9] he also served secondments as a special investigator with the Police Ombudsman for Northern Ireland, and was part of Lord Bonomy's review of corroboration.

[9] After being overlooked for the Chief Constable job when Phil Gormley was appointed as the successor to Stephen House in late 2015, he initially remained part of the force executive but in summer 2017 announced his intention to retire in the coming months.

[11] He then accepted a request to reconsider his decision after several allegations of misconduct were made against Chief Constable Gormley and the latter was placed on special leave;[12] by September 2017 Livingstone was leading the force on an interim basis.

In November 2023 Sir Iain took on the role of Officer in Overall Command of Kenova, a series of historical investigations and reviews in relation to the Troubles in Northern Ireland after his predecessor, Jon Boutcher was made Chief Constable of the PSNI.

In August 2024, following the publication of the Operation Kenova interim report, Sir Iain wrote to Secretary of State for Northern Ireland Hilary Benn to raise concerns after previously undisclosed material was made available by MI5.