When to Use ‘the Honourable’ (British Spelling)
The Honourable is used in direct address with e.g., a son of a viscount or baron; wife of the son of a viscount or baron; a younger son of an earl or viscount; wife of a younger son of an earl; daughter of an earl, viscount, or baron.
The Honourable is also used in direct address with many Canadian officials (below the rank of prime minister and deputy prime minister) and many Australian officials (including the prime minister and deputy prime minister.)
The Right Honourable is a courtesy title used with certain current and former Commonwealth officials such as members of the Queen’s Privy Council. It is typically abbreviated the Right Hon.
—–#1) The Honourable and the Right Honourable (both with a U like colour, flavour and armour) are British courtesy titles. The are not merely words to be translated – they are parts of a person’s name. Because it is considerate to write a person’s name exactly as he or she writes their name, use the British spelling with Commonwealth citizens and officials of former Commonwealth countries using British spellings.
—–#2) It is correct for an American to use the American spelling –– the Honorable –– with U.S. officials and officials of non-English speaking countries that use the Honorable as a courtesy title.
— Robert Hickey