Sir John Ernley (or Ernle; 1464 – 22 April 1520) was an English justice.
In his home county of Sussex he maintained a substantial legal practice, serving as feoffee, arbitrator, justice and commissioner, and joining the home assize circuit in 1496 and 1497 as an associate, followed by a position on the county bench in 1498.
After Sir Robert Rede died in 1519, Ernley was selected to replace him as Lord Chief Justice of the Court of Commons Pleas, and was appointed on 27 January of that year.
He served for barely a year, dying on 22 April 1520, and was buried in Sidlesham, near Chichester.
He left a son and heir, William Erneley, who also served as a Member of Parliament.