Ilbert was educated at Balliol College, Oxford, where he was Hertford, Ireland, Craven, and Eldon law scholar. He graduated with first class honours in Literae Humaniores and was elected a fellow of Balliol in 1864.
Ilbert was called to bar (Lincoln's Inn) in 1869. He joined the Parliamentary Counsel Office, the department for drafting parliamentary bills. He was a legal member of the Council of Governor-General of India from 1882-6. During this period he introduced the Ilbert Bill in 1883 for British India that proposed an amendment for existing laws in the country at the time to allow Indian judges and magistrates the jurisdiction to try British offenders in criminal cases at the District level, something that was disallowed at the time. He was appointed assistant parliamentary counsel to Treasury in 1886 and parliamentary counsel in 1899.