Carl was called to the Bar in 1993 and has spent the last twelve years as a government lawyer specialising in EU law and human rights. He has advised ministers and officials in many departments across a range of policy areas from tax to terrorism, from pensions to discrimination and from broadcasting to health. He has worked on major bills, on EU legislation and on litigation in the UK and Europe. Carl advised on the drafting of the European Constitution and represented the UK in negotiations, before moving to work with Lord Goldsmith at the Attorney General's Office.

Currently taking a break from his government legal career, Carl teaches at the National School of Government and BPP Law School, and writes the law blog Head of Legal.