Sir Peter Grain (1864 – 1947) was a British judge who served in Zanzibar, Egypt, Constantinople and China. He was the Chief Judge of the British Supreme Court for China from 1927 to 1933 and also judge of the High Court of Weihaiwei from 1926 to 1930.
Grain was born on September 25, 1864. He was the son of John Peter Grain, a well-known criminal barrister in London. He was called to the bar of the Middle Temple in January 1897.
Grain practiced in the criminal courts in London, sometimes as his father's junior, in England for 10 years. He was a member of the Bar Council from 1902 until 1906.
In 1906 at the age of 42, Grain commenced a career with the Foreign Office Judicial Service in Zanzibar. In 1906 he was made Resident Magistrate at Zanzibar, and the same year he was promoted to be Assistant Judge and a Judge of the Court of Appeal for East Africa. For a time he left the Bench to become Legal Member of Council and Attorney-General to the Government of Zanzibar, and he was for a short time, from August 1907 to April 1908 Acting First Minister there. He was awarded the Zanzibar Order of the Alijah, 1st class.
In 1910 he was made Assistant Judge of the British Supreme Consular Court at Constantinople; then Acting Judge in 1911. During World War I he was the Special Judge in Egypt for the trial of German and Austrian subjects and he was also Judge of the Prize Court there. In 1915, he became Assistant Judge and Acting Judge between 1917 and 1918 in the British Supreme Court for Egypt. He was appointed as Judge of the British Supreme Court for Egypt in 1919.