Sir William Johnstone Ritchie (October 28, 1813 – September 25, 1892) was one of the first judges appointed to the Supreme Court of Canada.

He graduated from the Pictou Academy and went to study law in Halifax in the office of his brother, John William Ritchie.

In keeping with his pledge to resign if a fellow Liberal candidate failed to win a by-election, he gave up his seat in 1851, only to be re-elected three years later.

He was appointed to the newly established Supreme Court of Canada on September 30, 1875, and became its chief justice on January 11, 1879.

She was the daughter of the late Captain Thomas L. Nicholson and his wife Amy (née Vernon) and stepdaughter of Vice-Admiral William Fitzwilliam Owen, R.N.