He was born at 6 King Street, St Marylebone, London, the son of Malcolm Donaldson (1884–1973), consultant gynaecologist, and his first wife, Evelyn Helen Marguerite, née Gilroy.

He joined the chambers of Sir Henry Willink, QC at 3 Essex Court and built a successful tort and commercial practice.

The trades unions, pointing to his Tory inclinations in his youth, nicknamed him "Black Jack", and 181 Members of Parliament (MPs) signed a House of Commons motion calling for his dismissal.

He replaced Lord Denning as Master of the Rolls and Records of the Chancery of England in 1982, becoming the presiding officer of the civil division of the Court of Appeal, where he pushed forward modernisation efforts, including the introduction of skeleton arguments in civil appeals, [clarification needed] judgments being "handed down" rather than read, and enhanced case management.

He presided over the trials of the Guildford Four in 1975 and the Maguire Seven in 1976, and was later criticised in Sir John May's interim report of his inquiry into the miscarriages of justice.

The inquiry by Sir John May into the injustice suffered by the Maguires said that Mr Justice Donaldson, as he was then, had failed to appreciate that the sudden emergence of new evidence on the last day of the trial removed the whole basis of the prosecution case.

[6] These remarks bore an uncanny resemblance to the words of another leading judge of the era, Sir Nigel Bridge, who commented in a similar IRA-based miscarriage of justice, the Birmingham Six trial, that he wished that he could still hang murderers.