The carrier’s obligation not to deviate from the agreed route during the carriage of goods by sea is generally recognized under international conventions and the maritime laws of many jurisdictions. Rather than providing a precise definition of deviation, these rules mainly specify the circumstances in which it is permitted. In practice, however, such exceptions have broadened the doctrine by allowing deviation where it is considered justifiable or reasonable. Judicial approaches to deviation vary among legal systems, with English common law developing the most advanced body of case law. This study examines how English courts have responded to the doctrine of deviation and identifies the key elements governing its application. Using a descriptive–analytical method and a systematic review of English judicial decisions, the study finds that English courts have gradually adapted the doctrine to the commercial and economic realities of international trade while remaining committed to fundamental principles of maritime law. The findings further indicate that Iranian law shares significant similarities with English law regarding deviation and may benefit from the experience of English courts in interpreting and developing its own legal framework.